矩阵尺寸必须一致但实际上相同

Question

I got an error message saying:

Matrix dimensions must agree.

Error in tankGame>exmRange (line 119)
    if (p1.dir == 'down') p1.value = imrotate(p1.oriValue, 180,'bilinear'); end

Yet I checked the size of p1.value and p1.oriValue , both of them are 32x32x3 . And if I delete this part the program runs perfectly.

I assume it's because imrotate somehow changed the dimension (although it shouldn't, for 180-degree square image rotation), so how can I fix it?

Answer 1

What is likely generating the error is p1.dir == 'down' . The == operator is an element-wise operator, it compares each of the characters in the two char vectors, yielding a boolean vector indicating which of the character pairs are equal. It is not doing a string comparison.

For example, if p1.dir is the char vector 'up ', then you are comparing a vector with 2 characters to one with 4 characters:

'up'=='down'   % generates the error message "Matrix dimensions must agree."
'doom'=='down' % returns the logical array [true true false false]

Use strcmp to compare strings:

if strcmp(p1.dir,'down')
   p1.value = imrotate(p1.oriValue, 180,'bilinear');
end

---

In newer versions of MATLAB (starting with R2016b) there is an actual string type (as opposed to the char vector that has always been called "string" in MATLAB). A string is created with double-quotes: "down" (as opposed to 'down' , which is a char vector). For this new type, the == operator does do a string comparison. When applying the operator to a string an a char vector, the char is converted to a string . So another solution would be to do this:

if p1.dir == "down"
   p1.value = imrotate(p1.oriValue, 180,'bilinear');
end