Why wont interpolation work

Im trying to interpolate some data with interp1 which looks like

10000 0.002078592

7943.282 0.001956255

6309.573 0.001852454

and so on. however later on there nans, which I have replace with zeros. Im continously getting the message 'The grid vectors are not strictly monotonic increasing.' This is the code im looking to fix

a=xlsread('EIS_data/DK40AH_25degC.xlsx');
b=xlsread('EIS_data/DK40AH_-5degC.xlsx');
c=xlsread('EIS_data/DK40AH_-10degC.xlsx');
d=xlsread('EIS_data/DK40AH_-20degC.xlsx');

%Replace nans

ix = isnan(a);
a(find(ix)) = 0;
ix = isnan(b);
b(find(ix)) = 0;
ix = isnan(c);
c(find(ix)) = 0;
ix = isnan(d);
d(find(ix)) = 0;

a1 = a(:,1);
a2 = a(:,2);
interp1q(a1,a2,frq)

any help would be appreciated.

Thanks

James

Answer 1

[Jan]

The error message tells you, that the first input of interp1 must be strictly monotonic increaing. When you insert some zeros in between, this is not the case.

What about removing the NaNs?

ix = isnan(a);
a(ix) = [];      % Faster without FIND
etc.