Meaning of the if statement

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Muhtasim Haque Nahian
评论： Muhtasim Haque Nahian 2021-5-9
function z = in_prod(x,y)
if size(x,2)==size(y,1)
z=x*y
else
z = "The inner dimensions are " + size(x,2) + " and " + size(y,1) + ". Matrix multiplication is not possible";
end
  • Can anyone explain me the meaning of this if statement please?
  • More specifically, why size(x,2) and size(y,1)? Why not size(x,any other value)?
TIA!
  1 个评论
Stephen23
Stephen23 2021-4-19
"More specifically, why size(x,2) and size(y,1)?"
Because matrix multiplication is only defined when those dimensions are equal:
https://en.wikipedia.org/wiki/Matrix_multiplication
http://mathworld.wolfram.com/MatrixMultiplication.html
"Why not size(x,any other value)?"
Because matrix multiplication is only defined for 2D matrices.

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回答（1 个）

David Fletcher
David Fletcher 2021-4-19
编辑：David Fletcher 2021-4-19
The if statement is checking that the number of columns in x (the number two in the argument of size is specifying that the function returns the number of columns) matches the number of rows in y (the number one in the argument of size is specifying that the function returns the number of rows). This ensures that matrix multiplication can be applied to x and y. If the inner dimensions do not match, the matrices cannot be multiplied.

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