Duplicate wave with arithmetic options

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Wed, 02/20/2019 - 12:57 pm

Greetings Forum,

I'm kind of new to programming with igor. I want to duplicate "wave k" to create "wave j" such that each point in "wave j" is subtracted from previous point in "wave k", something like this (image): 

It doesn't have to be a duplicate, I think one can define function to make this, any ideas how?

Thanks in advance.

 example of what i expect wave k to be like
•make/o/n=20 Original=p^2
•duplicate/o Original,Subtracted
•Subtracted[] = Original[p]-Original[p-1]

This can be easily done by the wave assignment in Igor Pro. You can see a demonstration by executing the above.

Here, p is the bin number of the waves, aligning the bin 1 of LHS to bin 1 of RHS, so and so forth. An assignment of Subtracted[] = Original[p] will make a bin-to-bin copy from Original to Subtracted. Now with the above, I am assigning them while doing the subtraction.

February 20, 2019 at 01:43 pm - Permalink

Duplicate/O k, j
j[0] = 0
j[1,] = k[p] - k[p-1]

This, of course, uses literal wave names in the commands. If you are using this inside a function, it is likely that the names should be variable. That adds some complexity.

For information about what all those square brackets and p's are doing: DisplayHelpTopic "Waveform Arithmetic and Assignment"

I would discourage wave names that are one character as they aren't very descriptive. And i, j, k are frequently used in programming as the index variables in loops. 

February 20, 2019 at 01:49 pm - Permalink

johnweeks wrote:

@Sandbo- be careful with point 0!

 

Thanks for pointing that out lol
At first I also wondered what will happen when it goes below zero, but somehow it worked. Maybe under some situation it will complain.

February 20, 2019 at 02:05 pm - Permalink

In Igor 8 I think the "index out of bounds" error is always turned on. In some previous version, it was only on if you added

#pragma rtErrors=3

at the top of your procedure file. In old versions, the point numbers were simply clipped to the range [0, npoints), leading to some strange and hard to find bugs.

February 20, 2019 at 02:12 pm - Permalink

Before reading the comments I was trying to figure out by myself, and came up with something like this:

Make /o /N=15 Kay =p +0
Duplicate /o Kay, Jay
InsertPoints 1,1, Jay
Make /o /N=15 KaySub
Kaysub = Kay - Jay

but the issue was the first element in J has to be 0 .....

and then with the help of my friend, wrote a do while loop as such:

Function KayJay()
variable Jay1,KayP1,KayM1
variable i=0
wave kay1
make/o/n=(numpnts(kay1)) Jay2
Wave Jay
Do
    If (i==0)
        Jay2[i]=0
   
    else
        Jay2[i]=Kay1[i]-Kay1[i-1]
    endif
Jay1=Jay2[i]
Kayp1=Kay1[i]
Kaym1=Kay1[i-1]
i+=1
While (i < numpnts(kay1))

End

 

Thanks a lot for your comments,

February 20, 2019 at 03:38 pm - Permalink

Just as food for thought: You can get rid of the if statement with initializing Jay2 with zero and write things more compact with a for loop.

Function KayJay()
    variable Jay1,KayP1,KayM1
    variable i=0
    Wave Kay1
    make/o/n=(numpnts(kay1)) Jay2=0
    Wave Jay
    For (i=1; i < numpnts(kay1); i+=1)
        Jay2[i]=Kay1[i]-Kay1[i-1]
        Jay1=Jay2[i]
        Kayp1=Kay1[i]
        Kaym1=Kay1[i-1]
    Endfor
End

Btw, your variables Jay1, KayP1, KayM1 and the wave 'Jay' is not used further in your function. Do they have any purpose?

February 25, 2019 at 08:57 pm - Permalink

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