How to work with interpolation function?

I am trying to do the interpolation between given set of data. I used interp1 function but it is showing the error as ''The grid vectors are not strictly monotonic increasing''

A=
290.21
291.22
291.11
290.73
293.03
299
304.92
323.5
323.63
322.93
323.35
327.91
334.71
338.42
354.02
353.05
354
359.45
367.48
368.58
368.28
382.41

B=
0.10855
0.11775
0.12746
0.13738
0.14831
0.16082
0.17539
0.32785
0.35750
0.38682
0.41663
0.44895
0.48715
0.52816
0.69683
0.70275
0.70755
0.71234
0.71765
0.72197
0.72559
0.75153

I write the code like this..

x=0.2:0.1:0.5

    D=interp1(B,A,x)

How to solve this problem??

Thanks

[Titus Edelhofer]

Hmm, I don't get an error for the values you gave ...

interp1(B,A,x)
ans =
  307.9192  320.1060  323.1157  335.8725

Titus

[R7 DR]

Thanks for the reply.

The strange thing is that if I am loading the the data from excel file it is showing error. It is working fine, if I make a column vector by copy & paste from excel.

I dont know the reason. Could you please try to load it from excel and check for the error?

Thanks for your time.

[Star Strider]

Your ‘A’ is not strictly monotonically increasing, but ‘B’ is. Your code works for me (in R2014b) as you wrote it. I got the same results Titus did.

[R7 DR]

How to deal with interpolation, in this case ‘A’ is not strictly monotonically increasing, but ‘B’.

[Star Strider]

The code you posted works. What do you want to do with your data and the interpolation? You have to tell us what the problem is.

[R7 DR]

Hi

I wrote the code like this, but showing the same error. I am attaching the excel file. could you please check once.

A=xlsread('interpolation.xlsx','sheet1','A:A')
B=xlsread('interpolation.xlsx','sheet1','B:B')

x=0.2:0.1:0.5

    D=interp1(B,A,x)

Thanks

Answer 1

[Titus Edelhofer]

Hi,

in your file B67 is equal to B68. Remove one of the lines.

Titus

[Titus Edelhofer]

No, since the data on x are not monotonic. Now it depends on the application, you can e.g. sort the data (using sort or sortrows), if this makes sense.

[R7 DR]

Is there any function to deal with the interpolation of these kind of data, becuae I cant modify the data.