Interpolation Error using interp1

I'm using a script to take these x and y values from a .txt file. At this point in the script the variables are assigned the fid is closed... When I code further, I'm trying to interpolate a user entered value which is called 'userx'.

Below, though, I am just trying to get it to interpolate at 100. I don't understand where my syntax error is.

>> x

x =

           0
          20
          22
          30
          33
          52
          52
          67
          84
         101
         103
         111
         116
         132
         141
         159
         162
         168
         171
         173

>> y

y =

        8477
       11886
       11384
        6087
        7871
        3003
        1941
        9213
       10981
        2179
        2219
         507
        1593
        8880
       11650
        4392
        6118
        4437
        2094
        1961

>> interp1(x,y,100) Error using interp1 (line 130) Values must be of type double or single.

>>

Answer 1

[Star Strider]

Check the data types of x and }y}. My guess is that they are either cells or strings.

If they are cells, you can convert them to double arrays with:

x = x{:};
y = y{:};

[Jorge Bastillo]

I have a two columned .txt file, my script asks the user for the file name, checks available files, and locates it. The user input variable is fileput. I then assign the left column as x and the right column as y.

fid=fopen(fileput,'r');
data=textscan(fid,'%d %d','headerlines',1); 
x=data{1}; 
y=data{2};
fclose(fid);

Now here in the command window I tried what you suggested... I think what you're saying is close to my problem.

>> x=x{:} Cell contents reference from a non-cell array object.

>> y=y{:}
Cell contents reference from a non-cell array object.

>> interp1(x,y,100)
Error using interp1 (line 130)
Values must be of type double or single.

>>

Not working though.

[Star Strider]

The output of textscan is a cell array, so your code should be giving you a numeric array. My best guess is that there are more than one header lines, or other problems with the file.

I would have to have your file to experiment with to understand the problem.

[Star Strider]

Jorge Bastillo’s ‘Answer’ moved here...

Also tried using cell2mat... Didn't work either.

>> a=cell2mat(x)
Cell contents reference from a non-cell array object.

Error in cell2mat (line 42)
cellclass = class(c{1});

[Star Strider]

That would mean to me that your conversion from cell to numeric with:

x=data{1}; 
y=data{2};

was successful (and correct), and that the problems are with non-numeric entries in ‘x’ and ‘y’.

Answer 2

[Image Analyst]

Try

x = double(x);
y = double(y);

to make sure they're doubles like interp1() said it wanted.