Using interp1 with semilog dataset

I have 3 arrays:

• 'Dose' contains 27 values ranging from 1x10^2 to 1x10^6
• 'AlThick' contains 27 values ranging from 0.0001 to 20
• 'Rays' contains 10000 values ranging from 0 to 20

The points in each data set are not equally spaced. Dose represents y values; AlThick and Rays both represent x values. I want to find the value of Dose for each non-zero value of Rays. I am doing the following and getting, as expected, 10000 values.

DoseMat = interp1(AlThick, Dose, rays(rays>0), 'linear')

However, I'm not sure if I need to be accounting for the fact that the y-axis data is plotted as a base-10 logarithm. I.e. it is a semilog plot with base-10 log values on the y-axis and linear values on the x-axis, as shown below.

Any advice is appreciated!

[Torsten]

And plotting "Dose" against "AlThick" in semilogy gives you a linear relationship ?

Could you include this plot ?

[Alex]

I have updated the OP with the plot of Dose vs AlThick

Answer 1

[Cris LaPierre]

You do not need to take account of the fact that you are plotting your data in a semilog plot. That doesn't impact how you would interpolate the data. The 'linear' here is the interpolation method.

However, you are not using interp1 correctly. Interp1 is for (x,y) data. The syntax is

• newY = interp1(knownX, knownY, newX, method).

You probably want to use interp2.

• newZ = interp1(knownX, knownY, knownZ, newX, newY, method).

[Alex]

Thank you for the fast reply. I think either I didn't explain myself properly in my original post, or I am misunderstanding your comment.

I believe my data is (x,y); AlThick is my x data and Dose is my y data. Rays is a set of 10000 values that represent different points on the x-axis (i.e. different values of AlThick), and I want to find the value of Dose for each of these 10000 points (unless it is 0, in which case it can be ignored).

Hopefully I'm explaining myself clearly!

[Cris LaPierre]

No, you are good, I just didn't read your post carefully enough. Then your syntax is fine, and the first paragraph of my answer addresses your other concern.

[Image Analyst]

@Alex, attaching data in a .mat file, and screenshots of it plotted, would help.

TUTORIAL: How to ask a question (on Answers) and get a fast answer

[Alex]

I've updated the OP with the plot of Dose vs AlThick