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An open source flight dynamics & control software library
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Generate Linear Model from XML Script #227

Open benhager opened 4 years ago

benhager commented 4 years ago

Does anyone have any experience with, or is it possible to generate a linear model via XML scripting? Looking to call into FGStateSpace to get x0, u0, A, B, C, D vectors. Thanks!

bcoconni commented 4 years ago

Your request is too vague. What do you mean by "generate a linear model" ?

bcoconni commented 4 years ago

No response from the issuer for 3 weeks: issue closed.

benhager commented 4 years ago

@bcoconni Sorry for the delay, i was not notified of a comment on this ticket. I thought generating a linear model is pretty standard, and I believe it is a part of the source code already. It is implemented in JSBSim Advanced Triming Branch by calling into FGLinearization.cpp.

The output should be something like this: `x0=.. [ 3.3500000001e+002; 1.0833708379e-001; 1.0833708380e-001; 0.0000000000e+000; -5.8423256804e-004; 0.0000000000e+000; 0.0000000000e+000; 0.0000000000e+000; 0.0000000000e+000; 0.0000000000e+000; 0.0000000000e+000; 1.5000000000e+002];

u0=.. [ 4.1507273608e-001; -3.5248398193e-003; -2.0575829692e-001; -2.9106407215e-003];

sys = syslin('c',.. [ -4.3427060360e-002, -9.8096550611e+000, -3.2087058179e+001, -2.0560557019e-010, 3.3305725641e+002, -1.8636402009e-002, -2.0618344994e-010, -2.1078986357e-010, 6.3607575515e-010, 2.0773530465e-010, -2.1567803515e-001, 1.4236057475e-005; -8.1166258462e-005, -1.3702931926e-001, 1.1657013512e-002, 1.0000000112e+000, -2.3830098715e-007, 1.5667392399e-005, 5.7283788879e-004, 6.2980734972e-005, -1.4375970466e-004, -1.7085689860e-007, -2.1476001587e-008, 3.9049977087e-007; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 1.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 6.0540241507e-036, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 4.8014340544e-005, -2.6971631568e+000, -1.9094256891e-002, -2.2374890325e+000, 6.2364254569e-001, -2.5663288773e-005, -9.2158761873e-004, -1.0519342025e-004, 2.3547930880e-004, 2.7986858924e-007, 3.0142651432e-008, -5.6196960641e-007; 3.2484363763e-007, 1.4609051075e-004, -2.0180142393e-004, -3.0944937006e-015, 7.3392437136e-006, 9.5220718213e-002, 1.0812528411e-001, -9.9413727569e-001, -6.0973949052e-013, -2.4168673428e-015, 1.4546616224e-004, -3.2639002901e-015; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 5.4871117678e-038, 0.0000000000e+000, 0.0000000000e+000, 1.0000000000e+000, 1.0876293119e-001, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 4.3186288961e-006, 3.6266092870e-002, -2.3172110931e-012, -1.5085023771e-005, -1.3973860910e+001, -3.2521186265e-011, -2.8602884424e+000, 2.5709013825e-002, 4.8483072664e-010, -1.7883824485e-011, -1.6154612370e-013, -2.1185981843e-008; -3.8410920579e-008, 2.7088800961e-003, 3.0836305031e-012, 1.5042210065e-005, 1.8357369617e+000, -4.5386746125e-010, -2.9805207306e-002, -3.9335120276e-001, 4.1956396647e-009, 2.3490235331e-012, 1.4995306610e-014, 1.8686946609e-010; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 3.0448632692e-036, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 1.0058972985e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; -2.7919215606e-011, -1.7922246605e-020, 1.1029074834e-020, 0.0000000000e+000, 0.0000000000e+000, -1.7309715278e-006, 0.0000000000e+000, 0.0000000000e+000, 1.6008943163e-005, 2.0413438883e-017, 0.0000000000e+000, 4.3213431698e-016; 4.7787890441e-008, 2.4281611155e-016, 1.2423149893e-016, 1.4117215788e-016, 9.0350181040e-017, -1.0112899773e-009, 1.4117215788e-016, 1.4117215788e-016, 9.3529470475e-009, 1.4117215788e-016, 9.3173624198e-017, -7.6492439679e-013; 1.3286536223e-010, -3.3500000001e+002, 3.3499994284e+002, 1.2199442845e-010, 1.2267097060e-010, 1.9457045900e-001, 1.6344275470e-010, 2.0440824959e-010, 1.7561183988e-010, 2.0440824959e-010, 3.8202369509e-010, 2.0440824959e-010],.. [ 2.5569127211e+001, 2.0899803878e-012, 1.5534093046e+000, -1.5323390704e-012; -1.1952405922e-003, 1.0162385181e-004, -8.7323683594e-003, 7.4279608648e-004; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 4.6836146026e-002, -1.6649632294e-004, -1.1821223004e+000, -1.2000347358e-003; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 1.6676965113e+000, 1.2463432217e-005, 5.3727331192e-001; 0.0000000000e+000, -1.4953362323e-003, 9.5942719514e-007, -3.6441188893e-001; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000],.. [ 1.0000000104e+000, 1.3737159558e-009, 7.0106883262e-009, 5.3053857603e-009, 6.4422541376e-009, 7.2949054205e-009, 5.3053857603e-009, 5.3053857603e-009, 6.5369931690e-009, 5.3053857603e-009, 4.8316906032e-009, 5.3053857603e-009; -9.1362103068e-013, 9.9999999998e-001, 1.9463597400e-011, -1.2143064332e-012, -2.7755575616e-013, -3.4694469520e-013, -1.6884641833e-012, -1.2143064332e-012, -3.0068540250e-013, -1.6653345369e-012, -1.1564823173e-012, -1.2143064332e-012; 0.0000000000e+000, -1.7066414254e-007, 1.0000000000e+000, 0.0000000000e+000, -1.5034270125e-013, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 4.0476881106e-013, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 1.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 1.8468480506e-012, 1.6424759411e-012, -1.6175392912e-012, 1.0751671544e-014, 1.0000000000e+000, 1.1021818585e-012, 1.0842021725e-014, 1.0842021725e-014, 4.1105718366e-012, 1.2988742026e-012, 9.9385199145e-015, -9.1723503792e-013; 0.0000000000e+000, 1.0337246237e-029, -7.7492183861e-029, 0.0000000000e+000, -3.2661079214e-017, 1.0000000000e+000, 4.0360161005e-032, 0.0000000000e+000, 0.0000000000e+000, 1.6028605840e-016, -8.9092157003e-048, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 1.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 1.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 4.1887902048e+004, 4.7123889804e+004, 0.0000000000e+000, 3.6650914292e+004, 5.2359877560e+003, 0.0000000000e+000, 0.0000000000e+000, -3.6650914292e+004, 4.7123889804e+004, 5.2359877560e+003, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 1.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 1.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 1.0000231365e+000],.. [ 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000]);

tfm = ss2tf(sys);

`

Please let me know if more information is needed. Generation a linear model at a flight condition is a commonly needed output in modern autopilot development processes.

seanmcleod commented 4 years ago

Taking a quick look I see FGLinearization.h and FGLinearization.cpp are in the current source tree in the initialization directory, however they are not referenced in CMakeLists.txt so they aren't included in the build currently.

seanmcleod commented 4 years ago

Also searching for FGLinearization in the Advanced Trimming Branch see https://github.com/arktools/jsbsim/search?q=FGLinearization&unscoped_q=FGLinearization comes up without any hits at all. I was trying to see how the linearization code is typically called.

agodemar commented 4 years ago

I confirm. This code comes from the great work by James Goppert, back in 2012. https://github.com/arktools/jsbsim

bcoconni commented 4 years ago

Taking a quick look I see FGLinearization.h and FGLinearization.cpp are in the current source tree in the initialization directory, however they are not referenced in CMakeLists.txt so they aren't included in the build currently.

Well they were at some point during JSBSim history (commits listed below with their messages because they are quite enlightening):

and then at some point Jon decided to remove all the code altogether:

Interestingly, the linearization code was supposed to be run by setting a mode value in the property /simulation/do_linearization https://github.com/JSBSim-Team/jsbsim/blob/d724427f1117794cf43662ec442c0f11477226e1/src/FGFDMExec.cpp#L157 and the linearization was made by calling FGLinearization https://github.com/JSBSim-Team/jsbsim/blob/d724427f1117794cf43662ec442c0f11477226e1/src/FGFDMExec.cpp#L1203-L1211 Another interesting point is that the documentation of DoLinearization stipulated that it should be called after the aircraft was trimmed https://github.com/JSBSim-Team/jsbsim/blob/d724427f1117794cf43662ec442c0f11477226e1/src/FGFDMExec.h#L470-L473 The good news are that we are not starting from a blank sheet. The bad news are that Jon's comment made it clear in the commit 0c739604464f0f3eaceda676d200f33c89b20180 (the one that removed James Goppert's code) that there were some problems with the code and I infer from that that we'd better know what we are doing before reintroducing this code in the current code base.

benhager commented 4 years ago

I am not surprised that you should trim the aircraft before running the linearization routine. This is a common stipulation, as linearization is only valid at a stable trim point.

seanmcleod commented 4 years ago

@jonsberndt can you shed any light on what the problems were in the code when you removed it via commit https://github.com/JSBSim-Team/jsbsim/commit/0c739604464f0f3eaceda676d200f33c89b20180?

In particular I guess if you remember any particular issues with the linearization code. If the issue was only/mainly with the trim code then maybe the linearization code could be used with the current trim code?

bcoconni commented 4 years ago

I have come across automatic differentiation which should also allow to generate a linear model with much more flexibility than what was done by FGLinearization. With that technique you can virtually derive any quantity with respect to any other quantity without needing to hard code the formula for that particular differentiation.

The concept is quite simple, you need to implement a new class for dual numbers and replace most of, if not all, occurrences of double in JSBSim by that new class. Nothing really difficult but that would need a decent, although not necessarily extensive, knowledge of C++ (at the very least class design and templating) and no particular familiarity with JSBSim overall architecture since it would be a low level modification.

Any thoughts ?

rega0051 commented 4 years ago

Very interested in bringing this feature back. Along with more control of trim options. The two features go hand in hand, relying on generation of jacobians, etc. One issue will be dealing with certain classes of nonlinearities in the actuator and sensor models. Disabling freeplay, deadband, error models, noise in the subsystems makes the results more representative of the desired system.

I'd like to help if help is needed.

seanmcleod commented 4 years ago

@rega0051 what additional control of the trim options are you looking for?

In terms of freeplay, deadband etc. if you don't want them included while generated the linearized model are you suggesting that the linearizing process automatically detect them and exclude them as opposed to you removing them from the model during the linearization process?

rega0051 commented 4 years ago

@seanmcleod As far as I know there isn't a means of either programmatically detecting or removing the presence of nonlinearities.

I've had many issues with the trim routines being hardcoded, I'm hopeful these issues won't propagate to the Linearization. A few of the issues off the top of my head: Trimming a flying wing without yaw control: can't use tFull, but tLongitudinal doesn't trim yaw at all (the desire is to have yaw trimmed with sideslip). The other recent issue I ran into is trimming a quad copter model in hover. The tCustom trim type would likely be useful, but there is no means of setting it up through a script or Python binding.

Goppert's Simplex linearization was also hardcoded if I recall (at least some of the parameters anyway, I think the GUI interface had ability to modify). The real difference with FGTrim is that the simplex algorithm will attempt to simultaneously minimize the objectives simultaneously.

seanmcleod commented 4 years ago

@agodemar I'm trying to remember/figure out the relationship between your paper - 'A General Solution to the Aircraft Trim Problem' - http://wpage.unina.it/agodemar/DSV-DQV/AIAA-2007-6703-905_DeMarco_Duke_Berndt.pdf and the trim code you mention in the paper to James Goppert's trimming code in - https://github.com/arktools/jsbsim

Was James's code an updated/improved version of what you describe in the paper?

And do you remember why @jonsberndt removed it in 2015? Had something changed between 2013 and 2015 with lack of maintenance etc. to stop it working?

bcoconni commented 4 years ago

@rega0051

Very interested in bringing this feature back. Along with more control of trim options. The two features go hand in hand, relying on generation of jacobians, etc. One issue will be dealing with certain classes of nonlinearities in the actuator and sensor models. Disabling freeplay, deadband, error models, noise in the subsystems makes the results more representative of the desired system.

I'd like to help if help is needed.

Of course, help is always very appreciated :smile: You're very welcome to submit proposals. Just make sure that we are on the same page before writing too much code. First things first, I would like to clarify what you are volunteering for ? Is it bringing back James Goppert's FGLinearization code as the original poster @benhager asked? Or is it about coding automatic differentiation as I have suggested above ? Not trying to push either way but we need to discuss the same topic to avoid misunderstandings.

As far as I know there isn't a means of either programmatically detecting or removing the presence of nonlinearities.

Well, it might not be possible to detect non linearities in general but we can detect the usage of FGActuator, FGDeadBand and the likes. Special handling can then be coded for these particular flight controls.

bcoconni commented 4 years ago

@seanmcleod There were at some point 3 different trim algorithms in JSBSim.

Legacy trim routines

These are the older (and the last still active) trim routines. They were designed by Tony Peden. The algorithm is quite simple: it trims one axis at the time. Of course this fails when local axis minima do not match the global minimum, hence the development of algorithms that targeted the global minimum by trying to minimize all axes simultaneously.

Files: src/initialization/FGTrim.h, src/initialization/FGTrim.cpp, src/initialization/FGTrimAxis.h and src/initialization/FGTrimAxis.cpp.

De Marco/Durke/Berndt's trim algorithm

These are implementing the algorithms described in the paper 'A General Solution to the Aircraft Trim Problem'. Even though its source code is still in JSBSim repository, it is no longer compiled and linked with JSBSim making it dead, unmaintained code.

Files: src/initialization/FGTrimAnalysis.h, src/initialization/FGTrimAnalysis.cpp, src/initialization/FGTrimAnalysisControl.h and src/initialization/FGTrimAnalysisControl.cpp.

Goppert's trim routines

As @rega0051 mentioned, these are using the Simplex algorithm to optimize all the axis simultaneously. The differentiation (aka linearization) is indeed hardcoded in FGLinearization and the trim routines themselves are managed by FGTrimmer and FGSimplexTrim. There again, even though the source code is still in JSBSim repository, it is no longer compiled and linked with JSBSim making it dead, unmaintained code.

Files: src/initialization/FGTrimmer.h, src/initialization/FGTrimmer.cpp,src/initialization/FGSimplexTrim.h, src/initialization/FGSimplexTrim.cpp, src/initialization/FGLinearization.h and src/initialization/FGLinearization.cpp.

In the case where some or all of these routines would be brought back to JSBSim, keep in mind that they also need some "glue" code in FGFDMExec to be summoned from scripts.

seanmcleod commented 4 years ago

@bcoconni thanks for the good summary.

I'm interested in trim routines that can potentially handle more cases than the current trim routines in JSBSim so I'll spend some time in a local branch adding Goppert's trim routines back in and testing them.

bcoconni commented 4 years ago

I'm interested in trim routines that can potentially handle more cases than the current trim routines in JSBSim so I'll spend some time in a local branch adding Goppert's trim routines back in and testing them.

Sure. That would be most interesting.

For the record, James Goppert has documented his algorithm in a document that is still accessible from the internet: On Some Trim Strategies for Nonlinear Aircraft Flight Dynamics Models with the Open Source Software JSBSim

Also note that James Goppert (@jgoppert) is on GitHub, no doubt he has some recollections about the algorithm he wrote almost 10 years ago :smiley:

seanmcleod commented 4 years ago

When I was searching yesterday I also came across a couple of YouTube videos he posted demonstrating the trim functionality via a GUI he produced and also generating linearized models and loading them up in Scicoslab.

https://www.youtube.com/watch?v=JCjRGJTWe5k

https://www.youtube.com/watch?v=-B0nQbcyo-o

jgoppert commented 4 years ago

I got sick of hidden states in the c++ code. For instance trying to track down states in a jet engine model. I would push you toward automatic differentiation. I was using numerical differentiation with a Nelder Mead Simplex for trimming. Also being able to obtain a human readable state name would be useful. Using AD and getting a 20 state model and not knowing why can be annoying. I found the Modelica language is a bit friendlier in this regard as it maps directly to a differential algebraic equation and supports AD, also see pymoca and casadi which supports AD. Casadi is a C++ AD library and maybe you could leverage it. Let me know how I can help.

agodemar commented 4 years ago

For the record, James Goppert has documented his algorithm in a document that is still accessible from the internet: On Some Trim Strategies for Nonlinear Aircraft Flight Dynamics Models with the Open Source Software JSBSim

For the record, that's a presentation I gave of a paper that @jgoppert and me co-authored quite a few years ago ;-)

bcoconni commented 4 years ago

For the record, that's a presentation I gave of a paper that @jgoppert and me co-authored quite a few years ago ;-)

Oops ! Sorry. And for the sake of completeness there was also a third author: Inseok Hwang 😉

bcoconni commented 4 years ago

After some more archeological unearthing, I found the following 2 discussions threads in the mailing list archives:

ermarch commented 3 years ago

This is just a heads up that the latest version of AeromatiC++ now also outputs the linear coefficients in JSON format. This might be enough for some uses.

bcoconni commented 3 years ago

This is just a heads up that the latest version of AeromatiC++ now also outputs the linear coefficients in JSON format. This might be enough for some uses.

@ermarch Just to clarify things : Aeromatic++ is not able to read an existing JSBSim model and build linear coefficients for any trimmed position, is it ?

ermarch commented 3 years ago

Yes that's correct, it can only calculate them from geometric data.

aarondewindt commented 3 years ago

I'm interested in using Goppert's linearization code (FGLinearization & FGStateSpace) to generate linear systems from the JSBsim models. Based on this thread I think there are more people who are interested in this as well. Since I'm planning on doing this either anyway, is there some specific way you'd like me to expose this functionality?

My plan for now was to add a DoLinearization function to FGFDMExec. This function would take in four std::vector< std::vector<double>> references to write the state space matrices to. I'm only planning on using this function through the python wrapper, so the next step for me would be to wrap this function so it returns 4 numpy arrays.

Do do this I want to do these modification to the FGLinearization class.

This will 100% break any code that already uses this, but I don't think will be an issue considering these files are currently not being included in the build.

I'll make pull request once I have something working. Are there any requested features?

agodemar commented 3 years ago

@aarondewindt That's a good start. Thanks. It would be great if you could double check the trimming features introduced by Goppert.

aarondewindt commented 3 years ago

I've exposed the linearization function to python. My plan is to spend the next few days testing and checking it out.

Are there any known issues with it by any chance? Jon mentions that the state space and linearization code stopped working, but I'm getting models out of it. I still need to see how valid they are though. @jgoppert and @jonsberndt, do either of you have any input or tips for me?

aarondewindt commented 3 years ago

@agodemar I might have a look at those at some point in the future, for now I'm focusing on the linearization part of it. From what I understand the issue that ended up with the Goppert's code being removed was with the linearization.

jgoppert commented 3 years ago

The biggest difficulty I had with this was hidden engine states etc. I remember having to trim and then having to simulate until the engine states settled down. The linearization was a rather straight forward finite difference approach. If there was a way to get it working with automatic differentiation it would be much better. Also automatically finding all states in the code would be a huge step forward.

bcoconni commented 3 years ago

@aarondewindt

This function would take in four std::vector< std::vector<double>> references to write the state space matrices

I suggest you use typedef or using to replace that ugly C++ code with something a bit more legible (in the JSBSim namespace of course)

using Matrix = std::std::vector< std::vector<double>>;

This will 100% break any code that already uses this, but I don't think will be an issue considering these files are currently not being included in the build.

Given that the feature is disabled for years and nobody complained until @benhager brought the topic 1 year ago, your feature is unlikely to break any code :smile:

I still need to see how valid they are though.

Yes, tests would be very much appreciated (just as you initiated with TestLinearization in your PR #370)

bcoconni commented 3 years ago

@jgoppert

If there was a way to get it working with automatic differentiation it would be much better.

I have some work in progress in my branch LinearSpace https://github.com/bcoconni/jsbsim/tree/LinearSpace where I am using dual numbers for automatic differentiation in JSBSim. At the moment, all the tests from the master branch pass and I can get the gradient of any property with respect to (almost) any property, but it remains to be checked if the gradient computations are correct. At the moment, the gradient of the dynamic pressure qbar with respect to the body velocity U is correct (i.e I get rho*U). That's a start :smile: I also plan to use Eugene L. Duke's Derivation and Definition of a Linear Aircraft Model to check the results I'm getting.

Furthermore, since every double occurrence must be replaced by a dual number instance, all the code of JSBSim is impacted. This means that the code needs to be maturated before finding its way to the master branch. In addition, automatic differentiation increases the amount of computations (twice as much since you need to compute the value and its gradient) so it cannot be enabled permanently. I need to find a way to enable it optionally without making the code a complete nightmare to read. Finally, there remains much to be done for the API. At the moment, you set the gradient of a property (say U aka velocities/u-fps) to 1.0 and JSBSim computes the gradients of all the variables with respect to U in parallel to its "normal" computations and that's it. No matrices/jacobians are built. You need to collect "manually" the gradients if you plan to get a matrix. As I said, this is WIP.

The work of @aarondewindt is useful in that we will be able to cross check the results from 2 different algorithms which is always useful. In addition, it will be the only way to get linearization matrices for a while :smile:

aarondewindt commented 3 years ago

@bcoconni

I suggest you use typedef or using to replace that ugly C++ code with something a bit more legible (in the JSBSim namespace of course)

Are you sure? Naming it matrix kinda implies it can be used for matrix calculations, but it's nothing more than an std::vector.

bcoconni commented 3 years ago

Are you sure? Naming it matrix kinda implies it can be used for matrix calculations, but it's nothing more than an std::vector.

Well, use whatever name you like which make the whole expression shorter !

bcoconni commented 3 years ago

@aarondewindt's patch has just been committed to the branch master. Finite difference linearization is now back in JSBSim ! Thanks Aaron and thanks also James who authored the original linearization code :+1:

At the moment,the easiest way to run the feature is with Python:

import jsbsim

fdm = jsbsim.FGFDMExec('.') # The path supplied to FGFDMExec is the location of the folders "aircraft", "engines" and "systems"

fdm.load_model('737') # Load the aircraft 737
fdm.load_ic('cruise_init.xml', True) # Load the initial conditions
fdm.run_ic() # Initialize the aircraft with initial conditions

# Set engines running
fdm['propulsion/engine[0]/set-running'] = 1
fdm['propulsion/engine[1]/set-running'] = 1
fdm.run()

# Trim
fdm['simulation/do_simple_trim'] = 1

# Linearization
linearization = jsbsim.FGLinearization(fdm)

print(linearization.system_matrix)
print(linearization.input_matrix)
print(linearization.output_matrix)
print(linearization.feedforward_matrix)
agodemar commented 3 years ago

That's great news. Thanks

sthelia commented 3 years ago

Hi, This is a great feature. I'm trying to replicate this but as soon as I include the linearization part I get an error. 

  File "/home/test/jsbsim-code2/test4.py", line 33, in <module>
    linearization = jsbsim.FGLinearization(fdm)
AttributeError: module 'jsbsim' has no attribute 'FGLinearization'

Do I have to do anything different to include the correct code? I'm running JSBSim 1.1.6.

seanmcleod commented 3 years ago

When and how did you install the python module for JSBSim? Maybe you've downloaded and built JSBSim 1.1.6 but you've previously done a pip install of JSBSim of an earlier version before the linearization was added?

sthelia commented 3 years ago

Yes, I have done a pip install of JSBSim, I don't remember when but sometime this spring, definitely after the Jan 15th comment. I did uninstall it and then reinstalled it today to see if that made any difference, but the error is still the same.

seanmcleod commented 3 years ago

My spring is at a very different time to your spring 😉

But I just double-checked and I can confirm that I see this issue after pip installing 1.1.6.

(base) C:\Users\Sean>pip install jsbsim
Collecting jsbsim
  Downloading JSBSim-1.1.6-320-cp37-cp37m-win_amd64.whl (767 kB)
     |████████████████████████████████| 767 kB 6.8 MB/s
Requirement already satisfied: numpy in c:\users\sean\anaconda3\lib\site-packages (from jsbsim) (1.18.1)
Installing collected packages: jsbsim
Successfully installed jsbsim-1.1.6
(base) C:\Users\Sean>

Trying to use FGLinearization, note the JSBSim build date of Apr 30 2021 and the confirmation of v1.1.6.

>>> import jsbsim
>>> fdm = jsbsim.FGFDMExec('.')

     JSBSim Flight Dynamics Model v1.1.6 [GitHub build 320/commit b477f6312bee2fd3af4c4e5ba1a3e732ed2b99d4] Apr 30 2021 12:00:59
            [JSBSim-ML v2.0]

JSBSim startup beginning ...

>>> linearization = jsbsim.FGLinearization(fdm)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'jsbsim' has no attribute 'FGLinearization'
>>>

It looks to me @bcoconni something went awry with the tagging of v1.1.6?

The master branch shows the linearization support being added to jsbsim.pyx.in and jsbsim.pxd on the 15th Jan, e.g.

https://github.com/JSBSim-Team/jsbsim/blob/master/python/jsbsim.pyx.in

However if you look at jsbsim.pyx.in and jsbsim.pxd for the v1.1.6 tag they're older than the 15th Jan, even though the v1.1.6 tag and version built is from Apr 2021?

https://github.com/JSBSim-Team/jsbsim/tree/v1.1.6/python

seanmcleod commented 3 years ago

However if you look at jsbsim.pyx.in and jsbsim.pxd for the v1.1.6 tag they're older than the 15th Jan, even though the v1.1.6 tag and version built is from Apr 2021?

Hmm, I assumed based on the build date of Apr 30 2021 and the following comment on https://github.com/JSBSim-Team/jsbsim/releases/tag/v1.1.6 that 1.1.6 was based on code in master on Apr 30.

github-actions released this 27 days ago · 164 commits to master since this release

However looking at the link to the 164 commits since - https://github.com/JSBSim-Team/jsbsim/compare/v1.1.6...master it looks like v1.1.6 is based on code from the beginning of Oct 2020, which would explain why it doesn't have any support for the linearization.

aarondewindt commented 3 years ago

@sthelia @seanmcleod I'm pretty sure the code currently in master is scheduled to be released with 1.2.0. If you look at the PROJECT_VERSION in the project root CMakeLists.txt it has version 1.2.0dev1. So you'll need to build and install the package from the repository instead of pip to use FGLinearization.

sthelia commented 3 years ago

@aarondewindt Alright, uninstalling with pip seemed to work! Thanks.

bcoconni commented 3 years ago

However looking at the link to the 164 commits since - v1.1.6...master it looks like v1.1.6 is based on code from the beginning of Oct 2020, which would explain why it doesn't have any support for the linearization.

Yes, correct. Releases v1.1.x are maintenance releases. The linearization feature is in 1.2.0dev1 as @aarondewindt pointed out.

@sthelia if you want to save yourself the burden of compiling JSBSim, you can download a Python wheel package from our Rolling Release and pick the file *.whl that match your platform and Python version. The file can then be installed with pip:

> pip install jsbsim --no-index -f /path/to/the/wheel/file.whl
seanmcleod commented 3 years ago

@sthelia just to confirm I followed @bcoconni's suggestion of downloading a wheel file from the rolling release, pip installed it and I was able to successfully run the linearization example that @bcoconni posted earlier in this thread.

GolgeA commented 1 year ago

sys = syslin('c',.. [ -4.3427060360e-002, -9.8096550611e+000, -3.2087058179e+001, -2.0560557019e-010, 3.3305725641e+002, -1.8636402009e-002, -2.0618344994e-010, -2.1078986357e-010, 6.3607575515e-010, 2.0773530465e-010, -2.1567803515e-001, 1.4236057475e-005; -8.1166258462e-005, -1.3702931926e-001, 1.1657013512e-002, 1.0000000112e+000, -2.3830098715e-007, 1.5667392399e-005, 5.7283788879e-004, 6.2980734972e-005, -1.4375970466e-004, -1.7085689860e-007, -2.1476001587e-008, 3.9049977087e-007; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 1.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 6.0540241507e-036, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 4.8014340544e-005, -2.6971631568e+000, -1.9094256891e-002, -2.2374890325e+000, 6.2364254569e-001, -2.5663288773e-005, -9.2158761873e-004, -1.0519342025e-004, 2.3547930880e-004, 2.7986858924e-007, 3.0142651432e-008, -5.6196960641e-007; 3.2484363763e-007, 1.4609051075e-004, -2.0180142393e-004, -3.0944937006e-015, 7.3392437136e-006, 9.5220718213e-002, 1.0812528411e-001, -9.9413727569e-001, -6.0973949052e-013, -2.4168673428e-015, 1.4546616224e-004, -3.2639002901e-015; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 5.4871117678e-038, 0.0000000000e+000, 0.0000000000e+000, 1.0000000000e+000, 1.0876293119e-001, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; 4.3186288961e-006, 3.6266092870e-002, -2.3172110931e-012, -1.5085023771e-005, -1.3973860910e+001, -3.2521186265e-011, -2.8602884424e+000, 2.5709013825e-002, 4.8483072664e-010, -1.7883824485e-011, -1.6154612370e-013, -2.1185981843e-008; -3.8410920579e-008, 2.7088800961e-003, 3.0836305031e-012, 1.5042210065e-005, 1.8357369617e+000, -4.5386746125e-010, -2.9805207306e-002, -3.9335120276e-001, 4.1956396647e-009, 2.3490235331e-012, 1.4995306610e-014, 1.8686946609e-010; 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 3.0448632692e-036, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 1.0058972985e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000, 0.0000000000e+000; -2.7919215606e-011, -1.7922246605e-020, 1.1029074834e-020, 0.0000000000e+000, 0.0000000000e+000, -1.7309715278e-006, 0.0000000000e+000, 0.0000000000e+000, 1.6008943163e-005, 2.0413438883e-017, 0.0000000000e+000, 4.3213431698e-016; 4.7787890441e-008, 2.4281611155e-016, 1.2423149893e-016, 1.4117215788e-016, 9.0350181040e-017, -1.0112899773e-009, 1.4117215788e-016, 1.4117215788e-016, 9.3529470475e-009, 1.4117215788e-016, 9.3173624198e-017, -7.6492439679e-013; 1.3286536223e-010, -3.3500000001e+002, 3.3499994284e+002, 1.2199442845e-010, 1.2267097060e-010, 1.9457045900e-001, 1.6344275470e-010, 2.0440824959e-010, 1.7561183988e-010, 2.0440824959e-010, 3.8202369509e-010, 2.0440824959e-010]

I've been looking at linear models for a few days too, and I saw a problem with this 12-state system matrix A. First three states of twelve are normally positions and they should have no effect on each other, sometimes last three states are positions but here for both conditions, position states are dependent to other positions which is seems inaccurate. Here I would like to know the order of the state variable or state variables column. Maybe the order of the states are different?

seanmcleod commented 1 year ago

sometimes last three states are positions

Looking at the order here it does look like the last 3 states are positions (lat, lon, alt).

https://github.com/JSBSim-Team/jsbsim/blob/c943e7817b06e0fd4eea05241b32ff00de879f7a/src/initialization/FGLinearization.cpp#L28-L58

pd3a commented 1 year ago

I tried doing the linearization but the trim failed. Could anyone help

fdm['simulation/do_simple_trim'] = 1 Full Trim

Trim failed Trim Results: Angle of Attack: 7.50 wdot: 3.22e+01 Tolerance: 1e-03 Failed Throttle: 0.50 udot: 1.35e+00 Tolerance: 1e-03 Failed Pitch Trim: 0.00 qdot: -4.53e-03 Tolerance: 1e-04 Failed Roll Angle: -0.00 vdot: 1.31e-15 Tolerance: 1e-03 Passed Ailerons: 0.00 pdot: 3.61e-22 Tolerance: 1e-04 Passed Rudder: 0.00 rdot: -1.01e-22 Tolerance: 1e-04 Passed Traceback (most recent call last): File "", line 1, in File "jsbsim.pyx", line 1058, in jsbsim.FGFDMExec.setitem File "jsbsim.pyx", line 1232, in jsbsim.FGFDMExec.set_property_value jsbsim.TrimFailureError: Trim Failed

seanmcleod commented 1 year ago

I tried doing the linearization but the trim failed

You haven't specified what aircraft you're using and what your initial conditions are. For example maybe you're trying to trim the 737 at 50kts, well you're never going to be able to generate a trim solution for that combination.