What is the purpose of this line in MATLAB's "factorial.m" function?

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Blake 2012-6-17

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EDIT: I have removed the rest of the FACTORIAL function in this post as per Jan's suggestion. To explain myself, I did consider whether posting a MATLAB function to Answers is copyright infringement. I didn't think so because the code is in MATLAB's language...and I didn't think it would be that helpful for a nefarious party to see a function in MATLAB like this. I may be mistaken, though, and will refrain from posting any MATLAB code from now on. But my question still stands...

I am confused about a line in MATLAB's FACTORIAL function. If you type "open factorial" in the command window and check (somewhere around) line 20, it says:

m = max([1; n(:)]);

n(:) is an array of real, nonnegative integers. 1 is appended to n(:) and that is passed to the MAX function...the only reason I can see for that 1 is to prevent MAX from returning 0 if n(:) consists entirely of 0's. But the rest of the code doesn't seem to require the MAX to return 1 instead of 0. What could be the purpose of this appended 1? I ask because I'm just learning MATLAB and may be mistaken in thinking this extra 1 is unnecessary.

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Jan 2012-6-17

It is surprising that you do not hesitate to publish the code of a toolbox function. Please read this again:

edit(fullfile(matlabroot, 'license.txt')), Software License Agreement, section 4.5.

Then I suggest to remove the source code fast.

Blake 2012-6-18

I have removed the code. I did consider whether posting a MATLAB function to Answers is copyright infringement. I didn't think so because the code is in MATLAB's language...and I didn't think it would be that helpful for a nefarious party to see a function in MATLAB like this. I may be mistaken, though, and will refrain from posting any MATLAB code from now on. But my question still stands, do you know whether that 1 is necessary and why?

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Answer 1

Blake 2012-6-19

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I believe the 1 is a remnant of the code before the author manually included an exception for 0 and 1 factorial. The author may have forgotten to remove it after changing a previous part, but since this doesn't cause an error, he may not have caught it (or left it in because it makes no difference).

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Answer 2

Geoff 2012-6-18

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I would hazard that it is there to handle the special case of computing zero-factorial, which of course is 1.

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Blake 2012-6-19

This was my first guess as well. But zero factorial is accounted for in the next line without this extra 1. The use of "m" in the next line is "cumprod(2:m)". 2:m returns an empty matrix whether m is 1 or 0.

I believe the 1 is a remnant of the code before the author manually included an exception for 0 and 1 factorial. The author may have forgotten to remove it after changing a previous part, but since this doesn't cause an error, he may not have caught it (or left it in because it makes no difference).

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