How to call individual column in a 2D wave

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Fri, 09/21/2012 - 10:29 am

Hi All,

I ran into this problem that I could not modify an individual column in a 2D wave.
For example, in a 1D wave, wave0, it is very straightforward if I want to add 1 to every row of the wave, i just input wave0=wave0+1. But I could not do the same thing to an individual column in a 2D wave, yw[][], say if I want to add 1 to the column 5, it always gave me an error message, saying expected operand. The command I put in is yw[][5]=yw[][5]+1.

Anyone's seen this before?

Thanks

Dimin
The problem is with the right hand side of your operator. Igor isn't quite sure what rows to deal with.
skyrock79 wrote:
Hi All,
yw[][5]=yw[][5]+1.


The two methods below work.

yw[][5]+=1

yw[][5] = yw[p][5]+1


in the second line, you can see that I used p to specify the rows. This means that for each row, we are adding 1 to the value previously in that row, instead of a different one.

September 21, 2012 at 10:34 am - Permalink

proland is right (as always:).

It helps to be able to put a wave assignment statement into words. Here is how I think about it.

The lefthand side of a wave assignment statement determines which points in the destination wave will be set. The righthand side determines what a specific point in the destination will be set to.

[] means "all rows" or "all columns" depending on where it occurs. Therefore this:
yw[][5]=<something>

means "set all rows, column 5, of yw to something".

[] on the righthand side would mean "all rows" or "all columns" but it makes no sense on the righthand side because Igor needs a specific value.

On the righthand side, "p" means "whatever row in the destination Igor is about to store into".
This:
yw[][5]=yw[p][5] + 1


means "set all rows of column 5 of yw to its current value (yw[p][5]) plus 1.

In this case, p will go from 0 to DimSize(yw,0)-1.

There is a similar internal index for columns: q. In this case q will go from 5 to 5.

This can also be written:
yw[][5] += 1

September 23, 2012 at 10:04 am - Permalink