Make a new wave by multiplying two others with all wavenames in variables?

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Mon, 07/01/2013 - 01:10 pm

I apologize for the very simple question, but this is driving me crazy. I'm just getting into igor programming. I've developed a multi file loading program (with help) that loads files made via a bash script (simple CSV format). Currently, two waves are imported (as there are two columns). The basename for the wave is derived from the file name and stored in a variable called "wav". So, the waves are named wav+"_" Then a number is placed after the names by igor. Obviously my two waves will be wav_0 and wav_1 filling in for the values of wav of course. I want to make a third wave "wav_2" that simply multiplies the two previous ones. The main line of code I've tried is:

$(wav+"_2")=$(wav+"_0")*$(wav+"_1")

I've tried every variation, with and without $, with the keyword "Wave" and a bunch of other things. I'm stumped. I've even tried assigning the values when the wave is made.

This line works fine.

Make/D $(wav+"_2")

While this one doesn't

Make/D $(wav+"_2")=$(wav+"_0")*$(wav+"_1")

Again, I apologize, this is extremely simple. I can do it on the command line just fine with the actual wave names, but not with the variables. Igor doesn't like my use of the $, but if I don't use it then igor doesn't know that I'm referring to a wave, correct?


As of right now, I've simply modified the bash script using awk to multiply the columns together. This works fine, but I'm trying to do as much of the arithmetic in igor. (For greater portability.)
Try this below. Shorter ways exist. This gives you a taste of the wave statement.

string wn0 = wav + "_0"
wave mw0 = $wn0
string wn1 = wav + "_1"
wave mw1 = $wn1
string wn2 = wav + "_2"
make/O/D $wn2
wave mw2 = $wn
mw2 = mw1*mw0


--
J. J. Weimer
Chemistry / Chemical & Materials Engineering, UAHuntsville

July 1, 2013 at 01:56 pm - Permalink

It may take some time before you can wrap your head around programming with waves, but it's actually not that difficult. To make it overly simple, you can think of it as names (strings) versus wave references (pointers). In your first line, you are basically just dropping names (the $ changes this, but only if you do specific things with the names like Make, Wave, Display etc.). So you first have to point Igor in the right direction via the Wave statement as J. J. Weimer already pointed out. Also note, that your pointer can but doesn't need to have the same name as the actual wave, see J. J.'s examples (I often see that this causes endless confusion for starters). You may want to read a bit about wave assignments, by invoking DisplayHelpTopic "Wave References".

July 2, 2013 at 06:21 am - Permalink

just a comment: I'd suggest to use Duplicate instead of Make for initialising the target array. Then you don't need to worry about the correct size of the latter.

July 3, 2013 at 03:21 am - Permalink