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Where is the problem

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john
john on 4 Jun 2012
Closed: MATLAB Answer Bot on 20 Aug 2021
Hi, I got this error:
In an assignment A(:) = B, the number of elements in A and B must be the same.
UserData.info(4,2)=num2cell(sym(strcat('u',sym(UserData.matrix{4,2}))));
UserData.info and UserData.matrix are cell type.
I don't understand, where is problem?
  1 Comment
Walter Roberson
Walter Roberson on 5 Jun 2012
I don't know what it would mean to strcat a string and a symbol. Unfortunately I do not have the toolbox to test with.

Answers (1)

per isakson
per isakson on 5 Jun 2012
Try
UserData.info{ 4, 2 } =num2cell(sym(strcat('u',sym(UserData.matrix{4,2}))));
--- next ---
It is easier to debug and understand with one step per line:
temp1 = UserData.matrix{4,2};
temp2 = sym(temp1);
temp3 = strcat( 'u', temp2 );
temp4 = sym( temp3 );
temp5 = num2cell( temp4 );
UserData.info{ 4, 2 } = temp5;
whos temp*
.
--- next 2 ---
Is strcat supposed to concatenate a character, 'u' and something of class sym? What is this strcat-line supposed to do?
.
--- next 3 ---
Run this function and note that strcat fails when temp2 == 10. '10' is displayed on screen before the error message.
function cssm
temp1 = UserData.matrix{4,2};
for temp1 = 3 : 23
temp2 = sym(temp1);
try
temp3 = strcat( 'u', temp2 );
catch me
disp( temp2 )
rethrow( me )
end
temp4 = sym( temp3 );
temp5 = num2cell( temp4 );
UserData.info{ 4, 2 } = temp5;
end
whos temp*
end
>> cssm
10
In an assignment A(:) = B, the number of elements in A and B
must be the same.
Error in strcat (line 95)
s(pos:pos+len-1) = str;
Error in cssm (line 7)
temp3 = strcat( 'u', temp2 );
>>
The reason is that length( temp2 ) always returns 1. Thus, it works for one digit numbers, but not for 10 or 23.
My conclusions are:
  1. the function, strcat, is made for strings only
  2. all the numerical stuff in Matlab isn't tested with sym class input. At Mathworks they didn't anticipate that someone would through sym at strcat :-).
  11 Comments
Walter Roberson
Walter Roberson on 5 Jun 2012
All those sym() conversions give the impression that you are converting back and forth more often than you need to.

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