Question about slice function

[Schultzer]

Hi,

First of all thanks for all this work. I have a question about https://github.com/R-js/blasjs/blob/b994277970ce64c90330859fdb65acc9194a14b6/src/lib/f_func.ts#L425

is there a reason why you would use undefined behavior here?

In the first round base + (i - rowStart) == -1 which result in a undefinedbehavior and then skips by one and turns the im = 0.

if this is the purpose wouldn't it be better to wrap it around an if statement to make it more clear what the desired behavior would be?

[jacobbogers]

Hello,

thank you for your interest,

first, its very clear, the code is wrapped in a small for loop, look what the starting (and ending) value of i is. just 4 lines above. (421)

for (let i = rowStart; i <= rowEnd; i++) {`     // <-- where "i" comes from
   // console.log(j, coorJ + i, base + i, r[coorJ + i]);
   re[base + i] = r[coorJ + i];
    if (this.i && im) {
         im[base + (i - rowStart)] = this.i[coorJ + i];   <-- the line of your prev question
    }
}

this makes base + (i - rowStart) == 0

The mapping is neccesary because, Not all langauges have zero based indexed arrays/matrices (fortran it is flexible and defaults to 1).

(rowBase and colbase properties) https://github.com/R-js/blasjs#matrix

[Schultzer]

If base + (i - rowStart) == 0 is assume to always return 0 on the first round, then I think we have a bug because when I added this line to the loop console.log(`re: base + i = ${base + i} im: base + (i - rowStart) = ${base + (i - rowStart)}`);

it clearly shows that on the first round base + (i - rowStart) = -1

fixtures.matrix_mxn(6, 6).slice(1, 6, 1, 6)
re: base + i = 0 im: base + (i - rowStart) = -1
re: base + i = 1 im: base + (i - rowStart) = 0
re: base + i = 2 im: base + (i - rowStart) = 1
re: base + i = 3 im: base + (i - rowStart) = 2
re: base + i = 4 im: base + (i - rowStart) = 3
re: base + i = 5 im: base + (i - rowStart) = 4
re: base + i = 6 im: base + (i - rowStart) = 5
re: base + i = 7 im: base + (i - rowStart) = 6
re: base + i = 8 im: base + (i - rowStart) = 7
re: base + i = 9 im: base + (i - rowStart) = 8
re: base + i = 10 im: base + (i - rowStart) = 9
re: base + i = 11 im: base + (i - rowStart) = 10
re: base + i = 12 im: base + (i - rowStart) = 11
re: base + i = 13 im: base + (i - rowStart) = 12
re: base + i = 14 im: base + (i - rowStart) = 13
re: base + i = 15 im: base + (i - rowStart) = 14
re: base + i = 16 im: base + (i - rowStart) = 15
re: base + i = 17 im: base + (i - rowStart) = 16
re: base + i = 18 im: base + (i - rowStart) = 17
re: base + i = 19 im: base + (i - rowStart) = 18
re: base + i = 20 im: base + (i - rowStart) = 19
re: base + i = 21 im: base + (i - rowStart) = 20
re: base + i = 22 im: base + (i - rowStart) = 21
re: base + i = 23 im: base + (i - rowStart) = 22
re: base + i = 24 im: base + (i - rowStart) = 23
re: base + i = 25 im: base + (i - rowStart) = 24
re: base + i = 26 im: base + (i - rowStart) = 25
re: base + i = 27 im: base + (i - rowStart) = 26
re: base + i = 28 im: base + (i - rowStart) = 27
re: base + i = 29 im: base + (i - rowStart) = 28
re: base + i = 30 im: base + (i - rowStart) = 29
re: base + i = 31 im: base + (i - rowStart) = 30
re: base + i = 32 im: base + (i - rowStart) = 31
re: base + i = 33 im: base + (i - rowStart) = 32
re: base + i = 34 im: base + (i - rowStart) = 33
re: base + i = 35 im: base + (i - rowStart) = 34
{ rowBase: 1,
  colBase: 1,
  nrCols: 6,
  nrRows: 6,
  r:
   Float64Array [
     1.2629542848807933,
     -0.3262333607056494,
     1.3297992629225006,
     1.2724293214294047,
     0.4146414344564082,
     -1.5399500419037095,
     -0.9285670347135381,
     -0.2947204467905602,
     -0.005767172747536955,
     2.404653388857951,
     0.7635934611404596,
     -0.7990092489893682,
     -1.1476570092363514,
     -0.28946157368822334,
     -0.29921511789731614,
     -0.411510832795067,
     0.2522234481561323,
     -0.8919211272845686,
     0.43568329935571865,
     -1.237538421929958,
     -0.22426788527830935,
     0.37739564598170106,
     0.1333363608148414,
     0.8041895097449078,
     -0.057106774383808755,
     0.5036079722337261,
     1.085769362145687,
     -0.6909538396968303,
     -1.2845993538721883,
     0.04672617218835198,
     -0.23570655643950122,
     -0.5428882550102544,
     -0.4333103174567822,
     -0.6494716467962331,
     0.726750747385451,
     1.1519117540872 ],
  i:
   Float64Array [
     -0.42951310949188126,
     1.2383041008533804,
     -0.2793462818542693,
     1.7579030898107073,
     0.5607460908880562,
     -0.4527839725531578,
     -0.8320432961178319,
     -1.166570547084707,
     -1.0655905803882961,
     -1.563782051071005,
     1.1565369971501793,
     0.8320471285723897,
     -0.22732869142475534,
     0.2661373616721048,
     -0.3767027185836281,
     2.4413646288945894,
     -0.7953391172553718,
     -0.054877473711578625,
     0.2501413228541527,
     0.6182432935662469,
     -0.17262350264585732,
     -2.2239002740099374,
     -1.263614384970583,
     0.3587288959713519,
     -0.011045478465663564,
     -0.9406491626186084,
     -0.11582532215695436,
     -0.8149687088699175,
     0.24226348085968588,
     -1.4250983947324998,
     0.36594112304921983,
     0.2484126488725964,
     0.06528818167162072,
     0.01915639166027384,
     0.2573383771555333,
     0 ],
  coord: [Function: coord],
  colOfEx: [Function: colOfEx],
  setCol: [Function: setCol],
  upperBand: [Function: upperBand],
  lowerBand: [Function: lowerBand],
  packedUpper: [Function: packedUpper],
  packedLower: [Function: packedLower],
  toArr: [Function: toArr],
  slice: [Function: slice],
  setLower: [Function: setLower],
  setUpper: [Function: setUpper],
  real: [Function: real],
  imaginary: [Function: imaginary] }

[jacobbogers]

I stand corrected, there actually several issues with that piece of code,
the

• -1 is hardcoded default offset of fortran index base "1" that should be changed to rowBase
• the rowStart needs to be corrected with the rowbase base + (i - (rowStart - rowBase)) (imaginary part)
• the real part is not correct base + i should be same as above

Will correct today and do some tests, then release, thanks for finding the issue

[jacobbogers]

version is now 1.0.12

Fixed