Calling a automatically generated vector valued function handle with a vector

Hello everyone,

I am frequently running into the following problem when I generate a function handle from a symbolic expression like in the following simplified example:

syms x
f = [x,0]
fh = matlabFunction(f) % this is equivalent to fh = @(x) [x,0.0] 
X = [1;2;3]
fh(X) 

The code above produces the obvious error:

Error using horzcat

Dimensions of arrays being concatenated are not consistent.

Error in symengine>@(x)[x,0.0]

Until now I used the 'File' option of matlabFunction and changed the definiton of the function inside the generated file to

fh = @(x) [x,0*x]

but this requires user intervention, which I want to avoid.

Can anybody think of a general solution wich dous not require user intervention and also works for an arbitrary number of collums returend by the function handle?

Thank you!

[Matt J]

when I generate a function handle from a symbolic expression like in the following simple example:

There don't appear to be any symbolic expressions in this example.

[Michael Gfrerer]

Sorry for being unclear. Now, I changed the question and provided the right context.

[Matt J]

But the only reason the function definition works in the symbolic domain is because x is a scalar. If this weren't the case, you would have the same problem, e.g.,

syms x [3,1]
f = [x,0]

Error using sym/cat>checkDimensions
CAT arguments dimensions not consistent.

Error in sym/cat>catMany (line 33)
[resz, ranges] = checkDimensions(sz,dim);

Error in sym/cat (line 25)
ySym = catMany(dim, args);

Error in sym/horzcat (line 19)
ySym = cat(2,args{:});

Answer 1

[Matt J]

Because the original symbolic function is defined only on R^1, you must post-vectorize the matlabFunction output.

syms x
f = [x,0];  %scalar form

fh = matlabFunction(f);

fh=@(x)   cell2mat( arrayfun(fh,x,'uni',0)); %add vectorization

fh([1;2;3]) 

ans = 3×2

1 0 2 0 3 0

[Michael Gfrerer]

Thank you for your answer!

Are you able to generalize this for an arbitray number of symbolic variables?

[Matt J]

Can you give an example?

Answer 2

[Walter Roberson]

No, there is no method at the moment other than hand manipulation.

I created a service request about related issues a couple of months ago. I suggest you also create a service request, as they prioritize in part according to how much user request there has been.