Extrapolation

[Sarah]

I want to do interpolation and extrapolation. I can interpolate by using
interp2 command. But, this command didn't perform extrapolation. Is there
any built-in function for extrapolation in octave? I have given an example
in detail. 

a= [ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13
14 15 16 17];
b= [ 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
0.001 0.001 0.001 0.001 0.001 0.011 0.011 0.011 0.011 0.011 0.011 0.011
0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011];
c= [ -0.88 -8.87 -0.86 -0.82 -0.77 -0.71 -0.66 -0.62 -0.57 -0.54 -0.50 -0.47
-0.44 -0.42 -0.39 -0.377 -0.36 -0.89 -0.88 -0.85 -0.81 -0.76 -0.71 -0.66
-0.61 -0.57 -0.53 -0.50 -0.47 -0.44 -0.42 -0.39  -0.37 -0.36];
cc = repmat(c,34,1);

ci= interp2(a, b, cc, 1.5, 0.0015) % Interpolation at some point

ai= [ 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5
12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 1 1.5 2 2.5 3 3.5 4 4.5 5
5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5
16 16.5 17 17.5];
bi= [ 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
0.001 0.001 0.001 0.001 0.001 0.001 0.0015 0.0015 0.0015 0.0015 0.0015
0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015 0.0015
0.0015 0.0017 0.0017 0.0017 0.0017 0.0017 0.0017 0.0017 0.0017 0.0017 0.0017
0.0017 0.0017 0.0017 0.0017 0.0017 0.0017 0.0017 0.011 0.011 0.011 0.011
0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011 0.011
0.011];
cim= interp2(a, b, cc, ai, bi) % Interpolation matrix


ce= interp2(a, b, cc, 18, 0.2)  % Extrapolation at some point

ae= 4* [ 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11
11.5 12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 1 1.5 2 2.5 3 3.5 4 4.5
5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15
15.5 16 16.5 17 17.5];
be= [ 0.101 0.101 0.101 0.101 0.101 0.101 0.101 0.101 0.101 0.101 0.101
0.101 0.101 0.101 0.101 0.101 0.101 0.1015 0.1015 0.1015 0.1015 0.1015
0.1015 0.1015 0.1015 0.1015 0.1015 0.1015 0.1015 0.1015 0.1015 0.1015 0.1015
0.1015 0.1017 0.1017 0.1017 0.1017 0.1017 0.1017 0.1017 0.1017 0.1017 0.1017
0.1017 0.1017 0.1017 0.1017 0.1017 0.1017 0.1017 0.111 0.111 0.111 0.111
0.111 0.111 0.111 0.111 0.111 0.111 0.111 0.111 0.111 0.111 0.111 0.111
0.111];
cem= interp2(a, b, cc, ae, be)  % Extrapolation matrix


How can I find 'ce' and 'cem' in this case?  Here, it gives "NA". How should
I extrapolate to find 'ce' and 'cem' ?

Thanks in advance

Sarah



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