MATLAB Answers

I think this is a documentation error

1 view (last 30 days)
Cynthia Moore
Cynthia Moore on 6 Apr 2020
Edited: per isakson on 6 Apr 2020
If I search the help for "array vs matrix", the 7th and 8th entries are rdivide and ldivide. I don't see a Quote button, so I'll post what I see there in a code block:
rdivide, ./ - Right array division
This MATLAB function divides each element of A by the corresponding element of B.
Documentation > MATLAB > Language Fundamentals > Operators and Elementary Operations > Arithmetic Operations
ldivide, .\ - Left array division
This MATLAB function divides each element of A by the corresponding element of B.
Documentation > MATLAB > Language Fundamentals > Operators and Elementary Operations > Arithmetic Operations
It seems to me that the secobd line under ldivide should be:
This MATLAB function divides each element of B by the corresponding element of A.
No? Shouldn't the A and B be reversed?

  1 Comment

per isakson
per isakson on 6 Apr 2020
Yes, it looks so, but in the description of ldivide the positions of A and B are switched. "x = B.\A divides each element of A by the corresponding element of B." Seems as if the search function replaces the formula by "This function". First of April was a week ago:)

Sign in to comment.

Answers (1)

Walter Roberson
Walter Roberson on 6 Apr 2020
No, ldivide says
B.\A divides each element of A by the corresponding element of B
whereas ldivide says
A./B divides each element of A by the corresponding element of B.
Notice that the order of A and B are reversed between the two of them.
>> [3 5].\[2 4]
ans =
0.666666666666667 0.8
And we see that the 2 from A (the second operand) was indeed divided by the 3 from B (the first operand)

  1 Comment

Cynthia Moore
Cynthia Moore on 6 Apr 2020
OK. The text in the search list is in agreement with the text in the separate function descriptions. Good. But, for me, the text is unneccessarily misleading. I suggest that the text in the search list should read:
rdivide, ./ - Right array division
A./B divides each element of A by the corresponding element of B.
Documentation > MATLAB > Language Fundamentals > Operators and Elementary Operations > Arithmetic Operations
ldivide, .\ - Left array division
A.\B divides each element of B by the corresponding element of A.
Documentation > MATLAB > Language Fundamentals > Operators and Elementary Operations > Arithmetic Operations
For most people, that would be enough of a description that they would not even need to read the full text. But if they did, both writeups should always have A as the first array and B as the second array (IMHO).

Sign in to comment.

Sign in to answer this question.