Problem with interp1 with data that occurs multiple times

I have two sets of data:

NMA =

    1.0000
    0.9568
    0.8540
    0.7553
    0.6755
    0.6031
    0.5388
    0.4828
    0.4412
    0.3944
    0.3344
    0.2973
    0.2648
    0.2199
    0.1967
    0.1715
    0.1543
    0.1371
    0.1126
    0.1019
    0.0869
    0.0689
    0.0602
    0.0433
    0.0338
    0.0339
    0.0276
    0.0253
    0.0113
    0.0125
    0.0177
    0.0139
    0.0191
    0.0212
    0.0212
    0.0307
    0.0277
    0.0160
    0.0279
    0.0506
    0.0676
    0.1110
    0.1188
    0.0995
    0.1156
    0.1323
    0.1104
    0.0528
    0.0981

and

XXX =

         0
    0.4938
    0.9875
    1.4813
    1.9751
    2.4689
    2.9626
    3.4564
    3.9502
    4.4440
    4.9377
    5.4315
    5.9253
    6.4190
    6.9128
    7.4066
    7.9004
    8.3941
    8.8879
    9.3817
    9.8754
   10.3692
   10.8630
   11.3568
   11.8505
   12.3443
   12.8381
   13.3319
   13.8256
   14.3194
   14.8132
   15.3069
   15.8007
   16.2945
   16.7883
   17.2820
   17.7758
   18.2696
   18.7634
   19.2571
   19.7509
   20.2447
   20.7384
   21.2322
   21.7260
   22.2198
   22.7135
   23.2073
   23.7011

I'm trying to interpolate to find the value for XXX wher NMA is equal to 0.1, but this happens multiple times and it's not showing me the first interpolated value:

I tried plotting like this:

MTF50=interp1(NMA,XXX,0.5);
MTF10=interp1(NMA,XXX,0.1);

plot([0,MTF50],[0.5,0.5],':','color','k')
plot([MTF50,MTF50],[0,0.5],':','color','k')
text(MTF50+max(XXX)/15,0.5,['mtf50 ',num2str(round(MTF50*100)/100)])

plot([0,MTF10],[0.1,0.1],':','color','k')
plot([MTF10,MTF10],[0,0.1],':','color','k')
text(MTF10+max(XXX)/15,0.1,['mtf10 ',num2str(round(MTF10*100)/100)])

for interpolating at 0.5 it still works because there is only one place where NMA "crosses" 0.5, but for 0.1 this is not the case:

this is the plot:

As you can see it doesn't show the first occasion where NMA crosses 0.1, and in the help I can't find a way to make interp1 give multiple outputs, is there a solution for this?

Kind regards

Thomas

[Ingrid]

I do not see how this code is working as to use interp1 the vectors should be strictly monotonic increasing which is clearly not the case

I would recommend using http://www.mathworks.com/matlabcentral/fileexchange/11837-fast-and-robust-curve-intersections instead and just give as a second curve a straight horizontal line at the value of interest

[Thomas Koelen]

Thanks, this worked:)