I need to find the isosbestic point between 20 pairs of UV spectra. This is too cumbersome to do it manually. Is there any way Igor can find the Isosbestic point between each pair automatically?
Assuming that your spectra are all measured with the same resolution you can concatenate the individual waves into a matrix and then look for a row that is a constant.
Identifying a constant row is easy in MatrixOP. Here is an example:
Suppose your data contains one constant row. You can generate such data using
A.G.'s comments are clever and concise. However, for real-world data, measurement error and noise may cause problems. You should supplement both methods by adding a tolerance in the comparison tests. Or for the second method, finding the row with minimum variance, and returning it and the variance for your inspection would also work.
... for real-world data, measurement error and noise may cause problems. You should supplement both methods by adding a tolerance in the comparison tests.
Within MatrixOP, the floor function and a tolerance factor can be used to impose a tolerance:
where numcols(ddd) converts the total variation to the average variation and a Tolerance of, say 100, restricts the average variation to be 0.01 or less.
Identifying a constant row is easy in MatrixOP. Here is an example:
Suppose your data contains one constant row. You can generate such data using
ddd[5][]=ddd[5][0]
edit ddd
Finding if a row is a constant using IP7 code:
Here aa will return the truth of a row being a constant.
Another possibility that is probably more efficient to calculate:
There are many other ways to determine if a row is constant but I hope this helps,
A.G.
WaveMetrics, Inc.
August 12, 2016 at 01:57 pm - Permalink
August 16, 2016 at 10:49 am - Permalink
Within MatrixOP, the
floorfunction and a tolerance factor can be used to impose a tolerance:MatrixOP/o dd=equal(floor((Tolerance/numcols(ddd))*sumRows(abs(ddd-colRepeat(sumRows(ddd)/numcols(ddd),numcols(ddd))))),0)where numcols(ddd) converts the total variation to the average variation and a Tolerance of, say 100, restricts the average variation to be 0.01 or less.
Alternatively,
dd = ee < .01 ? 1 : 0
would yield the same result and be slightly more legible, I think.
I don't have much experience with MatrixOP; are there easier ways to impose a tolerance?
This could also be done with
variance
MatrixOP/O ee=(VarCols(ddd^t))^tor standard deviation
MatrixOP/O ee=sqrt((VarCols(ddd^t))^t)depending on the desired result.
August 17, 2016 at 07:47 am - Permalink
There is really no need for the outer-most parenthesis but since you already typed them:
and you can do away with the slow second line of your code.
AG
August 17, 2016 at 01:10 pm - Permalink
Ah, I looked for something like that (
greater) but completely missed it. I see it's in IP6.38 as well as 7. Thanks.August 18, 2016 at 04:34 am - Permalink
MatrixOP has 162 functions so it is difficult to keep track. In IP7 you can execute
AG
August 18, 2016 at 10:23 am - Permalink