Storing variable names in a struct

Question

I am dealing with a rather large optimization problem (using MOSEK). To remind myself of the decision variables in this problem, I decided to try to store the variable names in a cell array in a struct, as desribed by MOSEK. However, I am unsure of how to do this. The relevant fragment of my code is listed below:

JiSet = 1:6; TiSet = [7 8]; nL = length(TiSet); 
P = struct;
P.names.var{1} = 'gamma_i(k+1)';    % my first constraint
P.names.var{2:1+nL,1} = cellstr(strcat('nu_',int2str(TiSet(:)),'(k+1)')); % a series of constraints of varying length

When I run the above code I get the following error:

The right hand side of this assignment has too few values to satisfy the left hand side.

However, if I enter strcat('nu_',int2str(TiSet(:)),'(k+1)') in my command window, it shows an ans variable that is a 2x1 cell (as desired). How do I assign the values in this cell to the 2:1+nL,1 entries in the P.names.var cell?

eigenchris · Accepted Answer · 2015-03-11 16:57:44Z

2

Try the same line with round brackets ( ), which are used to select sets of cells.

P.names.var(2:1+nL,1) = cellstr(strcat('nu_',int2str(TiSet(:)),'(k+1)'));

MyCell{1:2} refers to the literal contents of the cells.

MyCell = {10,24,-60};
MyCell{1:2}

ans =

    10


ans =

    24

MyCell(1:2) refers to a collection of cells.

MyCell(1:2)

ans = 

    [10]    [24]

Since cellstr(strcat('nu_',int2str(TiSet(:)),'(k+1)')); is a collection of cells, you need to assign it to a collection of cells, P.names.var(2:1+nL,1);

edited Mar 11, 2015 at 16:57

answered Mar 11, 2015 at 16:42

eigenchris

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Juderb · Accepted Answer · 2015-03-11 16:48:26Z

2

The problem is in how you structure your assignment in the last line. The right-hand side creates a single value, a 2x1 cell array. However, the left-hand refers to two separate fields. This behavior is likely a result of the nature of cell-arrays, which may except a different data-type in each cell. Cell arrays are set up to assign whatever is on the right-hand side to a single cell on the left-hand side. You can fix this with a simple modification:

P.names.var(2:1+nL,1) = cellstr(strcat('nu_',int2str(TiSet(:)),'(k+1)'));

This utilizes "array indexing" as opposed to "cell indexing".

answered Mar 11, 2015 at 16:48

Juderb

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