Interp1 error VqLite = F(Xqcol)

Question

Deanna 2023-2-16

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1913895-interp1-error-vqlite-f-xqcol

回答： Aditya Srikar 2023-3-2

Homework 2 Dropsonde Updated2.xlsx

clc;clear;
Filename= 'Homework 2 Dropsonde Updated2.xlsx';
T=readtable(Filename);
Warning: Column headers from the file were modified to make them valid MATLAB identifiers before creating variable names for the table. The original column headers are saved in the VariableDescriptions property.
Set 'VariableNamingRule' to 'preserve' to use the original column headers as table variable names.
T.AirTemp= T.AirTemp + 273.15;
%Humidity Graph After Converson 
R=T.RelHumid;
Temp= T.AirTemp;
p=T.AirPress;
A=[];
for i=1:length(R) 
Aval=6.12*(R(i)/100)*(exp((17.67*(Temp(i)-273.15))/(Temp(i)-29.65)))*(p(i)/1013.25);
A(end+1) = Aval;
end
A= A';
%figure(3)
%plot(A,T.GeopotenAltitude)
%Question 1a
N=[];
for i=1:length(Temp)
Nval= (77.6/Temp(i))*(p(i)+ ((4810*A(i))/Temp(i)));
N(end+1)= Nval;
end
N= N';
% figure(1)
% plot(N,T.GeopotenAltitude)
% title('ECE 6735 HW2 Problem 1a');
% xlabel('Refractivity (mbar)');
% ylabel('Altitude (m)');
%Question 1c
alt= T.GeopotenAltitude;
n0=interp1(alt,N,0);
angle= deg2rad(0.2);
deltaX= 0.2;
h=0;
x=0;
Re= 6371 *10^3;
while h< 1000
    alt 
    N
    h
    nh=interp1(alt,N,h);
    h= h+ deltaX* sqrt((angle^2)+(2*(nh+(h/Re)-n0)));
    x=x+deltaX;
end
alt = 376×1
1.0e+03 *

    2.6328
    2.6251
    2.6182
    2.6129
    2.6068
    2.6008
    2.5943
    2.5878
    2.5821
    2.5768
N = 376×1
  236.5111
  236.6743
  236.8167
  236.9778
  237.3261
  237.4599
  237.7228
  238.1719
  238.5314
  238.8193
h = 0
alt = 376×1
1.0e+03 *

    2.6328
    2.6251
    2.6182
    2.6129
    2.6068
    2.6008
    2.5943
    2.5878
    2.5821
    2.5768
N = 376×1
  236.5111
  236.6743
  236.8167
  236.9778
  237.3261
  237.4599
  237.7228
  238.1719
  238.5314
  238.8193
h = 6.9813e-04
alt = 376×1
1.0e+03 *

    2.6328
    2.6251
    2.6182
    2.6129
    2.6068
    2.6008
    2.5943
    2.5878
    2.5821
    2.5768
N = 376×1
  236.5111
  236.6743
  236.8167
  236.9778
  237.3261
  237.4599
  237.7228
  238.1719
  238.5314
  238.8193
h = 0.0007 + 0.0011i
Error using matlab.internal.math.interp1
Input coordinates must be real.

Error in interp1 (line 188)
        VqLite = matlab.internal.math.interp1(X,V,method,method,Xqcol);

So I am trying to create a code that takes in data from an exel and then uses the interp1 function to find the N value at that given height. I set h=0 sicne I am starting on the ground but when I use nh=interp1(alt, N, h) I get the error. When I use n0= interp1(alt, N, 0) I get an actual value.

I didnt think that using a variable instead of an actual value would matter if the variable had a number assigned to it.

Here is the error message:

Error in interp1 (line 152)

VqLite = F(Xqcol);

Error in ECE_6375_HW2_1 (line 45)

nh=interp1(alt,N,h);

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Torsten 2023-2-16

@Deanna

As you can see above, h in your code - defined as h= h+ deltaX* sqrt((angle^2)+(2*(nh+(h/Re)-n0))); - becomes complex-valued (most probably because (angle^2)+(2*(nh+(h/Re)-n0)) becomes negative).

Deanna 2023-2-16

Thank you! I did not catch that and thought there was something wrong with the variable.

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Answer 1

Aditya Srikar 2023-3-2

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1913895-interp1-error-vqlite-f-xqcol#answer_1183625

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Hi Deanna

Consider this statement in while-loop

h= h+ deltaX* sqrt((angle^2)+(2*(nh+(h/Re)-n0)));

The value angle^2 is always non-negative.

But if 2*(nh+(h/Re) < n0, then (2*(nh+(h/Re)-n0) becomes negative.

When (2*(nh+(h/Re)-n0) is negative and (angle^2)+(2*(nh+(h/Re)-n0)) also becomes negative, then the whole expression sqrt((angle^2)+(2*(nh+(h/Re)-n0))) would not be having any real roots and it will result in imaginary values as roots of the equation.

That’s the reason why you are getting an error

Error using matlab.internal.math.interp1

Input coordinates must be real.