Matlab Simplifies Function To 0

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Will
Will 2020-3-15
评论： Will 2020-3-15
Trying to create a sawtooth function using
sawtooth(x, a, f) = -a * mod((2 * x * f) + 1, 2) + a
but it simplifies to 0.
This function works fine in desmos, so I'm not sure why Matlab simplifies it to 0.
  2 个评论
Thiago Henrique Gomes Lobato
Thiago Henrique Gomes Lobato 2020-3-15
That's seems like a very strange bug, it seems matlab is simply ignoring the mod function, you can see this as an easier example by running:
A = mod(x*f,2)
A =
f*x
I'm really not sure why this happen, if you can live without the symbolic I would simply define a annonymous function:
sawtooth = @(x,a,f) -a * mod(( 2*(x) * f) + 1, 2) + a;
sawtooth(1.1,2,3)
ans =
-1.2000

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回答（1 个）

dpb
dpb 2020-3-15
That doesn't define a function in MATLAB syntax; it assigns the evaluation of the RHS of the assignment statement to a 3D array sawtooth presuming the variables x,f,a exist and are integer-valued and not zero.
One only defines a function in MATLAB in an m-file with a function statement at the beginning or as a variable with an anonymous function as
fnSawtooth=@(x,a,f) -a*mod(2*x*f+1,2)+a;
For the above functional, if x,f are single integer values, then mod(2xf+1,2) is always 1 and the expression reduces to -a*1+a --> -a+a --> 0.
NB: if have Signal Processing TB, there's a builtin sawtooth function in it...

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