How to define the size of output in subfunctions, for C coder

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PatrizioGraziosi 2020-12-30

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https://ww2.mathworks.cn/matlabcentral/answers/705513-how-to-define-the-size-of-output-in-subfunctions-for-c-coder

评论： Ryan Livingston 2021-1-1

在 MATLAB Online 中打开

Hello everybody,

I am experiencing an issue when porting a function to C with Matlab coder.

I have a function which runs inside a parfor parallel loop like

output = myfunction(id, mystruct) ;

where id is the parfor index and mystruct an input structure with one dimensional fields which are 1xn arrays, where n is variable.

inside myfunction there is a subfunction which is called inside myfunction like

output_temp = mysubfunction(mystruct.field)

where output_temp is a 1x1 variable.

Everything works in Matlab.

When I build code to port the function in C with Matlab coder, I get the following issue.

I define the input mystruct.field as unbound :1x:Inf, but at the "check for issues" stage, in the mysubfunction the coder sees mystruct.field as :Infx:Inf so that the coder sees output_temp as :1x:Inf instead of 1x1, and this generates an error. I am run out of ideas and cannot fix this...

Can you help me in fixing this, please?

Thanks in advance,

Patrizio

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PatrizioGraziosi 2020-12-31

编辑：PatrizioGraziosi 2020-12-31

在 MATLAB Online 中打开

Hi Ryan,

I am focusing the problem.

Once the code is generated, the MEX is built, at testing level I get the following error when calling the following local function

function [ one_over_tau_x_temp ] = my_local_funct(Skk, e, I, z, DOSf, vf_x, v_x_k)
                                    
    one_over_tau_temp_array(:) = z .* Skk .* DOSf./e .* I .* (1-vf_x./v_x_k);
    
    one_over_tau_x_temp = 1/(2*pi)^3 .* sum(one_over_tau_temp_array);
end

where

z, Skk , e, v_x_k

are 1x1 while

DOSf, I , vf_x

are :1x:Inf

I want

one_over_tau_temp_array

to be 1x:Inf but

z .* Skk .* DOSf./e .* I .* (1-vf_x./v_x_k);

turns to be 1x1.

It must be a task of arrays multiplication due to some different size spec, in Matlab this is not an issue but in the C coder it looks it is.

However, I modified the code to make

DOSf, I , vf_x

to be 1x:Inf but still

z .* Skk .* DOSf./e .* I .* (1-vf_x./v_x_k);

appears to be 1x1.

Thus, I'm doing concatenated array and scalar multiplication and the result is an array in matlab but a scalar in the code...

Any clue?

In similar yet opposite way, when I call another local function

function [ one_over_tau_x_temp_array] = ...
                                    my_locl_funct_2(Skk, e, I, z, DOSf, vf_x, v_x_k, )
    
    one_over_tau_x_temp_array = Inf(1,size(vf_x,2));
    
    one_over_tau_x_temp_array(:) = z .* Skk .* DOSf./e .* I .* (1 - vf_x./v_x_k); 
end

I get the opposite error:

one_over_tau_x_temp_array is reas as [1] [1]

whereas z .* Skk .* DOSf./e .* I .* (1 - vf_x./v_x_k) is a [1][n] array, as should be...

I really cannot figure out why

z .* Skk .* DOSf./e .* I .* (1 - vf_x./v_x_k)

is a [1][1] in the first local function and [1][n] in the second one..

Thanks in advance

Patrizio

Ryan Livingston 2020-12-31

在 MATLAB Online 中打开

I took your my_local_funct and put it in a separate file to try with codegen:

function [ one_over_tau_x_temp ] = my_local_funct(Skk, e, I, z, DOSf, vf_x, v_x_k)
                                    
    one_over_tau_temp_array = z .* Skk .* DOSf./e .* I .* (1-vf_x./v_x_k);
    
    one_over_tau_x_temp = 1/(2*pi)^3 .* sum(one_over_tau_temp_array);
end
>> t = coder.typeof(1,[1, Inf], [1,1]);
>> codegen my_local_funct -args {1,1,t,1,t,t,1} -report

Looking at the report shows that Coder computed the size of one_over_tau_temp_array to be :1x:Inf as expected. Screenshot from clicking the "View report link":

Do you see similar sizes when you look at the report for your larger example?

Assuming so, I continued on. When I then try to run the generated MEX I get an error:

>> vec = 1:3;
>> my_local_funct(1,1,vec,1,vec,vec,1)
ans =
   -0.0887
>> my_local_funct_mex(1,1,vec,1,vec,vec,1)
Error using sumprod (line 46)
The dimension to operate along was selected automatically, is variable-length, and has length 1 at run time. This is not supported. Manually
select the dimension to operate along by supplying the DIM argument.

Is that what you're seeing? Or do you get a different error?

PatrizioGraziosi 2020-12-31

Hi Ryan,

many thanks for the support!

So, when I run the matlab function I see the following sizes for one run, as example (the 2046 can vary from few ones to tens of thousands)

z 1 1

Skk 1 1

DOSf 1 2046

e 1 1

vf_x 1 2046

v_x_k 1 1

one_over_tau_temp_array 1 2046

one_over_tau_x_temp 1 1

If I run the MEX file I get the same until v_x_k, then the code crashes with the error

Error using tau_calc_funct_ELECTRA_C_v0>tau_ODP_funct (line 1119)

Sizes mismatch: [1][1866] ~= [1][1].

More information

line 1119 is where the code does the multiplication

one_over_tau_temp_array = z .* Skk .* DOSf./e .* I .* (1-vf_x./v_x_k);

and the "More information" links to the "Incompatibility with MATLAB for Scalar Expansion" doc page. It looks that the z .* Skk .* DOSf./e .* I .* (1-vf_x./v_x_k) returns a scalar, although before doing this the sizes are as in Matlab

Forgive me one question, I'm using the coder to port in C the function file, where there is a function and, at the end the local function. That is, in the coder GUI app I call the function file, inside this file there are a main function plus the local functions, is this correct?

Thanks

Patrizio

PatrizioGraziosi 2020-12-31

编辑：PatrizioGraziosi 2020-12-31

在 MATLAB Online 中打开

Hi Ryan,

I think I got a clue. The issue that I detected was due to the variable 'I', which can be a 1D array but inside the local function only a scalar is entered, so inside the local function I modified as follows

one_over_tau_temp_array = Inf(1,size(vf_x,2)); 
           
one_over_tau_temp_array(1,:) = z .* Skk * I(1) * DOSf/e .* (1-vf_x./v_x_k);

Then I got the same error as you, but it was located after processing the results as I was summing a 2D varable 'V',

sum(sum( V ))

whereas I understand it is necessary to specify the sum dimensions like

sum(sum( V, 1), 2).

Now the specific local function looks fine, I'll implement this finding to all the local functions and I'll see...

I'm grateful to you for having accompained me in debugging my file, thank you so much!!!

I wish you a happy new year,

Patrizio

Ryan Livingston 2021-1-1

Excellent! Happy new year Patrizio!

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How to define the size of output in subfunctions, for C coder

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