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Interp1 returns NaN for all values

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Hi, my code seems to be returning NaN for all values of Tractive_effort_V1, Tractive_effort_V2 etc.. Im not sure why its returning NaN instead of values. Any help would be greatly appreciated.
Here is my code so far:
Engine_Speed = [1000, 1250, 1500, 1600, 1750, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6200, 6500];
Engine_Torque = [156.0784, 200.4152, 289.3725, 306.2588, 322.3529, 357.6471, 357.6471, 357.6471, 357.6471, 357.6471, 357.6471, 353.1313, 358.2166, 352.1367, 326.1142, 261.8453];
Gear_Ratios = [3.4100, 2.0500, 1.4300, 1.1000, 0.9000, 0.7900];
V = (1:0.25:75);
Fd = 0.5*rho*Cd*A*V.^2+Vehicle_Mass*g*(ad+bd*V);
Vehicle_speed_1 = (Engine_Speed*Rolling_Radius)/((Gear_Ratios(1)*Final_Drive_Ratio)*2*pi/60);
Vehicle_speed_2 = (Engine_Speed*Rolling_Radius)/((Gear_Ratios(2)*Final_Drive_Ratio)*2*pi/60);
Vehicle_speed_3 = (Engine_Speed*Rolling_Radius)/((Gear_Ratios(3)*Final_Drive_Ratio)*2*pi/60);
Vehicle_speed_4 = (Engine_Speed*Rolling_Radius)/((Gear_Ratios(4)*Final_Drive_Ratio)*2*pi/60);
Vehicle_speed_5 = (Engine_Speed*Rolling_Radius)/((Gear_Ratios(5)*Final_Drive_Ratio)*2*pi/60);
Vehicle_speed_6 = (Engine_Speed*Rolling_Radius)/((Gear_Ratios(6)*Final_Drive_Ratio)*2*pi/60);
Tractive_effort_1 = (Engine_Torque*Final_Drive_Ratio*Gear_Ratios(1)*trans_eff/Rolling_Radius);
Tractive_effort_2 = (Engine_Torque*Final_Drive_Ratio*Gear_Ratios(2)*trans_eff/Rolling_Radius);
Tractive_effort_3 = (Engine_Torque*Final_Drive_Ratio*Gear_Ratios(3)*trans_eff/Rolling_Radius);
Tractive_effort_4 = (Engine_Torque*Final_Drive_Ratio*Gear_Ratios(4)*trans_eff/Rolling_Radius);
Tractive_effort_5 = (Engine_Torque*Final_Drive_Ratio*Gear_Ratios(5)*trans_eff/Rolling_Radius);
Tractive_effort_6 = (Engine_Torque*Final_Drive_Ratio*Gear_Ratios(6)*trans_eff/Rolling_Radius);
Tractive_effort_V1 = interp1(Vehicle_speed_1,Tractive_effort_1,V);
Tractive_effort_V2 = interp1(Vehicle_speed_2,Tractive_effort_2,V);
Tractive_effort_V3 = interp1(Vehicle_speed_3,Tractive_effort_3,V);
Tractive_effort_V4 = interp1(Vehicle_speed_4,Tractive_effort_4,V);
Tractive_effort_V5 = interp1(Vehicle_speed_5,Tractive_effort_5,V);
Tractive_effort_V6 = interp1(Vehicle_speed_6,Tractive_effort_6,V);

Accepted Answer

Abolfazl Chaman Motlagh
Abolfazl Chaman Motlagh on 8 Dec 2021
According to documentation of interp1. the function returns NaN for points outside the domain. so check V and See if it's point are inside of domain Vehicle_speed. even if not by option 'extrap' you can make function to return specific number by extrapolation. for example :
interp1([1 2],[2 4],0.5)
ans = NaN
interp1([1 2],[2 4],0.5,'linear','extrap')
ans = 1
you can see it returns a number.
so add option 'extrap'. like :
Tractive_effort_V1 = interp1(Vehicle_speed_1,Tractive_effort_1,V,'linear','extrap');
but i recommend check your variables first, because it seems you want interpolation, not extrapolation.
  3 Comments
Abolfazl Chaman Motlagh
Abolfazl Chaman Motlagh on 8 Dec 2021
Hi, Happy to Help.
As you can see for example in Vehicle_speed_1 lowest value is 0.2890e+03 equal to 289. and highest is 1878.3. but in your code V which are the point you want to use interp1 on to find their value are between 1 and 75.
V = (1:0.25:75);
so this is why interp1 return NaN for all values. all of V points (query points) are outside of domain.
you can eather choose V points inside your domain ( for example here for Vehicle_speed_1 between 289 and 1873.3) or use 'extrap' as i mentioned before for extrapolation.
Amelia Hanson
Amelia Hanson on 8 Dec 2021
Oh thank you so much, Vehicle_speed should be between 1 and 75 not 289 and 1873.3, I missed out a sign in one of the equations which is why its going wrong. Thank you!

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