how to interpolate for increasing - decreasing type of data set

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Aditya Gandhi
Aditya Gandhi on 1 Jul 2021
Edited: Stephen23 on 1 Jul 2021
i am trying to get result for following code however I get NaN as result. Please help me correct my code
rpm1=[1000,2000,2500,3000,3500,4000,4500,4750,5320,5800,6000]; %engine rpm from table
theta1=[100;80;60;40;20;1]; %throttle from table
tr1=[117.200000000000,123.600000000000,129.100000000000,132.100000000000,134.300000000000,137.200000000000,134.800000000000,135.200000000000,129,119.300000000000,113.100000000000;115.300000000000,121.900000000000,127.300000000000,131.100000000000,120.500000000000,125.500000000000,124.500000000000,125.100000000000,118.800000000000,109.600000000000,104.700000000000;106,103.600000000000,96.7000000000000,89.6000000000000,86.4000000000000,80.9000000000000,74,69.8000000000000,55.7000000000000,45.8000000000000,41.2000000000000;98,85.9000000000000,77.6000000000000,69.3000000000000,63.8000000000000,56.9000000000000,50.5000000000000,46,32.2000000000000,21.3000000000000,17.4000000000000;65.4000000000000,45.7000000000000,37.2000000000000,27.8000000000000,23.5000000000000,19.1000000000000,15.6000000000000,11.9000000000000,0,0,0;0,0,0,0,0,0,0,0,0,0,0]; %torque from table
rpm1out=[1000;1400;1700;1900;3300;3500;3700;4100;4700;4900;5200;5400]; %sample rpm
tr1out=[95.4929658551372;102.313891987647;101.110199140734;100.518911426460;115.749049521378;122.776670385176;129.044548452888;128.100320049574;121.905913857622;126.674342460896;128.548223266531;127.323954473516]; %sample torque
theta1out=interp2(rpm1,theta1,tr1,rpm1out,tr1out); %desired throttle values for sample rpm and sample torque values
  3 Comments
Stephen23
Stephen23 on 1 Jul 2021
"I did not understand the approach you suggested earlier."
I did not suggest a complete approach; I recommended where you could start looking.
"Please can you refer me to a similar exaple if possible."

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Answers (3)

Chunru
Chunru on 1 Jul 2021
Since tr1out is outside the range of theta1, you are doing extropolation as well. For the default interpolation method, the extrapolated values are NaN. To generate some extrapolated data, specify a different interpolation method such as spline. Be careful to use the extropolated data!!
rpm1=[1000,2000,2500,3000,3500,4000,4500,4750,5320,5800,6000]; %engine rpm from table
theta1=[100;80;60;40;20;1]; %throttle from table
tr1=[117.200000000000,123.600000000000,129.100000000000,132.100000000000,134.300000000000,137.200000000000,134.800000000000,135.200000000000,129,119.300000000000,113.100000000000;115.300000000000,121.900000000000,127.300000000000,131.100000000000,120.500000000000,125.500000000000,124.500000000000,125.100000000000,118.800000000000,109.600000000000,104.700000000000;106,103.600000000000,96.7000000000000,89.6000000000000,86.4000000000000,80.9000000000000,74,69.8000000000000,55.7000000000000,45.8000000000000,41.2000000000000;98,85.9000000000000,77.6000000000000,69.3000000000000,63.8000000000000,56.9000000000000,50.5000000000000,46,32.2000000000000,21.3000000000000,17.4000000000000;65.4000000000000,45.7000000000000,37.2000000000000,27.8000000000000,23.5000000000000,19.1000000000000,15.6000000000000,11.9000000000000,0,0,0;0,0,0,0,0,0,0,0,0,0,0]; %torque from table
rpm1out=[1000;1400;1700;1900;3300;3500;3700;4100;4700;4900;5200;5400]; %sample rpm
tr1out=[95.4929658551372;102.313891987647;101.110199140734;100.518911426460;115.749049521378;122.776670385176;129.044548452888;128.100320049574;121.905913857622;126.674342460896;128.548223266531;127.323954473516]; %sample torque
theta1out=interp2(rpm1,theta1,tr1,rpm1out,tr1out, 'spline'); %desire

Yazan
Yazan on 1 Jul 2021
The function interp2 performs interpolation for 2D gridded data. It has the form Vq = interp2(X,Y,V,Xq,Yq), where X and Y contain the coordinates of the sample points. V contains the corresponding function values at each sample point. Xq and Yq contain the coordinates of the query points. Now, in your example, the 2D function tr1 is defined over rpm1 and theta1, but those two vectors have different sizes! You have stored 11 values in rpm1 and only 6 values in theta1. For interp2 to function properly, you should define the missing 5 theta1 values.

KSSV
KSSV on 1 Jul 2021
Edited: KSSV on 1 Jul 2021
rpm1=[1000,2000,2500,3000,3500,4000,4500,4750,5320,5800,6000]; %engine rpm from table
theta1=[100;80;60;40;20;1]; %throttle from table
tr1=[117.200000000000,123.600000000000,129.100000000000,132.100000000000,134.300000000000,137.200000000000,134.800000000000,135.200000000000,129,119.300000000000,113.100000000000;115.300000000000,121.900000000000,127.300000000000,131.100000000000,120.500000000000,125.500000000000,124.500000000000,125.100000000000,118.800000000000,109.600000000000,104.700000000000;106,103.600000000000,96.7000000000000,89.6000000000000,86.4000000000000,80.9000000000000,74,69.8000000000000,55.7000000000000,45.8000000000000,41.2000000000000;98,85.9000000000000,77.6000000000000,69.3000000000000,63.8000000000000,56.9000000000000,50.5000000000000,46,32.2000000000000,21.3000000000000,17.4000000000000;65.4000000000000,45.7000000000000,37.2000000000000,27.8000000000000,23.5000000000000,19.1000000000000,15.6000000000000,11.9000000000000,0,0,0;0,0,0,0,0,0,0,0,0,0,0]; %torque from table
rpm1out=[1000;1400;1700;1900;3300;3500;3700;4100;4700;4900;5200;5400]; %sample rpm
tr1out=[95.4929658551372;102.313891987647;101.110199140734;100.518911426460;115.749049521378;122.776670385176;129.044548452888;128.100320049574;121.905913857622;126.674342460896;128.548223266531;127.323954473516]; %sample torque
[X,Y] = meshgrid(rpm1,theta1) ;
plot(X,Y,'.r')
hold on
plot(rpm1out,tr1out,'*k')
theta1out=interp2(X,Y,tr1,rpm1out,tr1out); %desired throttle values for sample rpm and sample torque values
If you see, the values which you are trying to seek using interp2 are falling outside the domain. So this comes under extrapolation and results cannot be trusted.
  3 Comments
Aditya Gandhi
Aditya Gandhi on 1 Jul 2021
No Sir. My problem is not resolved. I am still trying to figure out what how this can be done.

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