(x) v.s. (num) in the manual

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Mon, 08/11/2008 - 03:55 am

I am confused about the notations (x) and (num) in Volume V "Reference" of IgorMan.pdf. For example, I don't see any difference between the properties of the variables of the built-in operations digamma(x) and gamma(num). They worked the same way as I assigned independent variable x to them when I tried to do Curve Fitting; no problem found. So what is the difference between "x" and "num"? Thanks.
It might not answer your whole question, but I should point out that "x" is a function in IGOR as well :-), it allows one to access the scaling of a wave in an expression. For example the following expression would fill each point in the ypoints wave with a value that was calculated from the digamma function, using the x scaling at that point.

Wave ypoints
ypoints=digamma(x)

Try typing Displayhelptopic "x" for more information. You could do exactly the same thing with the gamma function:

Wave ypoints
ypoints=gamma(x)

THe use of any inbuilt function name as a local variable should be avoided, viz. x,y,p,q,r,s,z,t.

August 11, 2008 at 02:17 pm - Permalink

isend wrote:
I am confused about the notations (x) and (num) in Volume V "Reference" of IgorMan.pdf. For example, I don't see any difference between the properties of the variables of the built-in operations digamma(x) and gamma(num). They worked the same way as I assigned independent variable x to them when I tried to do Curve Fitting; no problem found. So what is the difference between "x" and "num"? Thanks.


In this case I think the difference is in the authorship of the particular documentation involved. The function gamma() has been in Igor for a long time, and was probably written by Larry, Howard, or Jim. The digamma() function was added recently by AG. In this case, the use of "x" as the built-in function to access the X index during a wave assignment is a red herring.

We should be more consistent...

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com

August 12, 2008 at 10:42 am - Permalink

Thank you. I have done a lot of wave scaling with x, too. I think the manual uses different variable notations x and num for digamma and gamma for a reason, but I have not figured the reason out...

(Oh, thank you for the clarification, johnweeks. I did not see your reply until I posted mine.)

August 12, 2008 at 11:00 am - Permalink