sbmlsecretary
commented
10 years ago I accept the issue as valid, and agree with the proposed change.
I frequently encounter the same issue, for example with analytic volumes in the spatial package, where it is very convenient to write expressions like: 10gt(x,10)lt(x,20), rather than the corresponding piecewise expression.
Admittedly, you loose some error checking, but i have yet to encounter a situation, where that warning would have helped.
Original comment by: fbergmann
I hate to introduce this so late in the proceedings, but hey, if not now, then never...
There are many simulators (if not all of them) that will accept SBML with mixed-type math, that is, mathematical functions that return booleans being used in a numeric context, with 'true' meaning '1' and 'false' meaning '0'. As an example, every time Herbert writes an equation for a wave, he always writes something like:
squareWave = amplitude(gt(sin(2pi*time/period),0)) + center
Now, it's perfectly possible to re-write this equation using the 'piecewise' function, but it's more awkward, and no simulator that we could find seems to mind. (Copasi will warn you that there's an error, but will still simulate it, for example, and both Frank's roadrunner and the new libroadrunner accept it without comment.)
This would also allow mixed type parameters. I have often, in my own simple modeling, found myself wanting a parameter to be a boolean, but cannot actually say things like:
Event: at (time>3): isOn=true;
Instead, I have to set 'isOn' to '1', and then check 'if(isOn==1)' later, which is a bit awkward (though again, not insurmountable).
A change like this might benefit the 'qual' package as well, since it can have non-numeric elements with discrete values (including boolean values, unless I'm mistaken).
If accepted, I would want to say something explicit in the spec, like, "A boolean value of 'true' takes the value of '1' in a numeric context, and 'false' takes the value of '0'. If a boolean value is being assigned to, '0' implies 'false', and all other values (positive and negative) imply 'true'."
(I don't know if we have any contexts where you can assign a value to a boolean number--perhaps not.)
Reported by: luciansmith
Original Ticket: sbml/sbml-specifications//273