Interpolating a set of values

Hi,

I have datasheet with known temperatures, resistances and I have another set of resistance values that needs to be converetd into temperatures using the datasheet. I want to linearly interperolate each resistance values so I get its corresponding temperatures.

I am new to matlab. Any help on this would be appreciated. I have also attached the code I have for now (Note: all values are stored in an excel file).

%%
Datasheet=xlsread('name_of_sheet.xlsx','Sheet2');
known_Resistance=Datasheet(:,2);
known_Temp=Datasheet(:,1);
Meaured_Resistance=Datasheet(:,3);
Time=Datasheet(:,4);

Temp=interp1(known_Resistance,known_Temp,Meaured_Resistance);

plot(time,Temp)
%%

Thank you.

[Torsten]

And what' your problem ? Does your code not work ?

[AA]

Yes, the code doesn't work. Below is the error I am getting.

%%Error using griddedInterpolant

The sample points must be finite.

Error in interp1 (line 136)

F = griddedInterpolant(X,V(:,1),method);

%%

[Voss]

@AA Perhaps you can upload the excel file (using the button with the paperclip icon) so that we can try to reproduce the error?

[AA]

Sheet 2 of the attached file.

[Torsten]

@AA

And did you check the data from your sheet whether they contain Inf or Nan values as MATLAB told you to do ?

Answer 1

[Voss]

The problem is that xlsread returns a matrix with some NaNs since the data columns in the xlsx file do not all have the same amount of data:

unzip('name_of_sheet.xlsx.zip')
Datasheet=xlsread('name_of_sheet.xlsx','Sheet2');
disp(Datasheet(95:110,:));

   94.0000    1.1390   11.5054   12.6866
   95.0000    1.1100   11.0665   12.6872
   96.0000    1.0810   11.5004   12.8538
   97.0000    1.0530   11.5735   12.8539
   98.0000    1.0270   11.5735   12.8545
   99.0000    1.0010   11.5011   13.0211
  100.0000    0.9753   11.5776   13.0212
       NaN       NaN   11.1309   13.0217
       NaN       NaN   11.4958   13.1884
       NaN       NaN   11.5716   13.1885
       NaN       NaN   11.1290   13.1890
       NaN       NaN   11.5058   13.3557
       NaN       NaN   11.5829   13.3558
       NaN       NaN   11.1383   13.3563
       NaN       NaN    7.9365   16.0230
       NaN       NaN    7.9187   16.0231

One solution is to remove those NaNs from your variables before doing the interpolation:

known_Resistance=Datasheet(:,2);
known_Temp=Datasheet(:,1);
Meaured_Resistance=Datasheet(:,3);
Time=Datasheet(:,4);

% remove NaNs:
known_Resistance = known_Resistance(~isnan(known_Resistance));
known_Temp = known_Temp(~isnan(known_Temp));
Meaured_Resistance = Meaured_Resistance(~isnan(Meaured_Resistance)); % these two don't have NaNs
Time = Time(~isnan(Time));                                           % but what the hell

Temp=interp1(known_Resistance,known_Temp,Meaured_Resistance);

% plot(time,Temp)
plot(Time,Temp)

[AA]

Thank you so much!

[Voss]

You're welcome! If you have any questions let me know. Otherwise, if my answer works, please click 'Accept this Answer'. Thanks!