# solving two-variable matrix function

2 views (last 30 days)
Dmitry Solomatin on 14 Dec 2022
Commented: Jiri Hajek on 14 Dec 2022
Hi,
so assume I have a function like this:
f = [x(1) + x(2) ; x(2) * x(1)]
and my x = [2; -2]
how can I solve it? feval doesnt work for some reason ("Dimensions of arrays being concatenated are not consistent)

Jiri Hajek on 14 Dec 2022
Hi this can be done using inline function very efficiently like this:
fh=@(x,y)[x+y,x*y];
fh(2,-2)
ans = 1×2
0 -4
Dmitry Solomatin on 14 Dec 2022
Thanks it now works, but for some reason this gives me a 1x3 matrix and it should only 1x2?
fh = @ (x,y) [2*x- 400*x*(-x^2+y) -2, 200 * (y-x^2)];
fh(2,-2)
Jiri Hajek on 14 Dec 2022
This is because Matlab interprets space within brackets as a separator of vector elements, same as a comma. You can eithertake away all the spaces or put your expressions into parentheses. That way, you can forget about the meaning of spaces:
fh = @ (x,y) [(2*x- 400*x*(-x^2+y) -2), (200 * (y-x^2))]
fh = function_handle with value:
@(x,y)[(2*x-400*x*(-x^2+y)-2),(200*(y-x^2))]
fh(2,-2)
ans = 1×2
4802 -1200

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