Generate mex code for a MATLAB function containing other mex functions (R2011a)

For example, I've already generated the mex code for the following function (trying to minimize built-in MATLAB function calls, hence the custom cross product code here):

function supX = getSuperCross(v)

%#codegen

supX = [0    -v(3)  v(2);
        v(3)  0    -v(1);
       -v(2)  v(1)  0];

end

Which works fine when called as getSuperCross_mex. Now I want to generate mex code for another function which calls getSuperCross in its mex form.

Original code:

function R = getRotation(axis, angleRad)

R = eye(3) + getSuperCross(axis)*sin(angleRad) + (1 - cos(angleRad))*(axis*axis' - eye(3));

end

Attempt at mex generation:

function R = getRotation(axis, angleRad)

%#codegen

supX = coder.nullcopy(zeros(3,3));
coder.ceval('getSuperCross_mex',coder.wref(supX),axis);
R = eye(3) + supX*sin(angleRad) + (1 - cos(angleRad))*(axis*axis' - eye(3));

end

I get a few different errors trying different implementations (as I'm 100% on how this works)

If code looks as given: "Build error: Compilation returned error status code 2. See the target build log for further details." --> "...8 Writing library for getRotation_mex.mexw32, 9 Error GETROTATION.C 52 undefined reference to _getSuperCross_mex, 10 gmake: * [getRotation_mex.mexw32] Error 1"

Including a supX= before the coder.ceval call with and without the coder.wref inside: "Not a scalar location; C function calls always return scalar values." which I though would be solved by the coder.nullcopy call.

Hopefully my issue is clear here, how am I supposed to call this getSuperCross_mex so it isn't generating more code than I need? I've tried to implement coder.extrinsic with no success and have started to look into mexCallMATLAB.

Thanks in advanced for any help!

Answer 1

[Kaustubha Govind]

How about just:

function R = getRotation(axis, angleRad)

coder.extrinsic('getSuperCross_mex');
temp = zeros(3,3); %expected output type of getSuperCross_mex
temp = getSuperCross_mex(axis);
R = eye(3) + temp*sin(angleRad) + (1 - cos(angleRad))*(axis*axis' - eye(3));

end

Since you're simply generating another MEX file from getRotation (and not standalone code to be run outside of MATLAB), MATLAB Coder will know to simply call back into the MATLAB Engine for getSuperCross_mex.

[Alex]

Thanks for the reply!

This gives an error of "Expected either a logical, char, int, fi, single, or double. Found a MATLAB type. MATLAB types are returned from calls to the MATLAB interpreter and are not supported inside expressions. They may only be used on the right-hand side of assignments and as arguments to MATLAB calls."

I remember seeing a function dealing with MATLAB types in mex (?), but can't seem to find it..

[Kaustubha Govind]

Ah. It's because MATLAB Coder doesn't know what type getSuperCross_mex(axis) returns. It might be best to pre-allocate an intermediate variable to the expected type. Please see my update answer above.

[Bob Dart]

What if he wanted to build a getRotation.dll file? How would he invoke his getSuperCross_mex then?

Thanks!