MATLAB Coder giving out-of-bounds error for struct

Question

I am trying to MEX some code by using MATLAB's coder toolkit. The code initially had cell arrays in it which is not handled by the coder at the moment, so I decided to use structs in compensation for that.

My issue is that the size of the struct is not fixed, and herein lies the problem. What I have essentially is this:

Temp= struct('a',"some variable");
for i = 2:x
    Temp(j).('a') = Temp(i-1).('a')*Temp(1).('a');
end

In the command window of MATLAB, this would be completely acceptable, however when trying to build the MEX file, it throws this error:

Index expression out of bounds. Attempted to access element 2. The valid range is 1-1.

Is there a way to fix this, or is there another solution to 'cell array' like structures that the coder will allow?

ThP · Accepted Answer · 2014-09-18 20:32:49Z

2

You can use repmat:

MyStruct = repmat(Temp,1,N);

where N is a constant (i.e. hard-coded, not data-dependent).
Then, if you wish,

for i=2:N
    MyStruct(i).a = MyStruct(i-1).a*MyStruct(1).a;
end

No need for MyStruct(i).('a')

answered Sep 18, 2014 at 20:32

ThP

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6 Comments

Amro Over a year ago

+1 here are some relevant links to docs: Define Arrays of Structures for Code Generation, Index Substructures and Fields. Any way, it seems to me that the entire structure could be replaced with a regular numeric array

ThP Over a year ago

@Amro: For the simple example the OP provided, I agree.

G Boggs Over a year ago

@ThP That worked thanks! I now have another problem though. Some of the variables I am trying to store in struct are complex. It now comes up with the error saying: "Cannot assign a complex value into a non-complex location." Is there a way to fix this?

Amro Over a year ago

@GBoggs: try initializing with a complex constant when you first create the structure, so something like: Temp = struct('a',complex(0,0));. See: Code Generation for Complex Data

Amro Over a year ago

@GBoggs: See this page: Diagnose and Fix Variable-Size Data Errors. Also read the section in the docs that explains variable-size data.

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