Why am I getting this interp1 error?

%% AEM 588 HW1 Question 2
clear all;
close all;
clc;
global A_const;
global B_const;
global C_const;
mu = 398600; %km^3/s^2
% % nu0 = 1e-3;
Isp = 100;
r0 = 2378 + 12800; %km
m0 = 8; %kg
T = 12/1000;
v0 = sqrt(mu/r0);
rho0 =1;
tau0 = 0;
nu0 = T/m0/9.81;
T0 = nu0*(mu*m0)/r0^2*1000.;
mdot = T0/Isp/9.81;
A_const = T0*r0^2/1000;
B_const = mu*m0;
C_const = mdot*sqrt(mu*r0^3);

tspan = [0 10000];
initialConditions = [1.;0.;1.];

%Solve ODE
[tau,rho] = ode45(@odefun,tspan,initialConditions);
t = tau;
r = rho(:,1);
rMoonNorm = ones(length(r),1).*(384400/r0);
b_line = polyfit(t,rMoonNorm,1);
y_line2 = polyval(b_line,t);
x_int = interp1((y_line2-r),t,0);

Error using matlab.internal.math.interp1
The sample points must be finite.

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

y_int = polyval(b_line,x_int);

figure(1); clf(1);
plot(t,r)
hold on
plot(t,rMoonNorm)
xlabel('Time, Non-Dimensional')
ylabel('Radius, Non-Dimensional')

t = tau./sqrt(mu/r0^3);
r = rho(:,1).*r0;
rMoon = ones(length(r),1).*384400;
time_intercept = x_int/sqrt(mu/r0^3);
hours_intercept = time_intercept/3600;
days_intercept = hours_intercept/24;
Prop_mass = mdot*time_intercept;
fun = @(x) T0./(m0-mdot*x)
dV = integral(fun,0,time_intercept);

figure(2); clf(2);
plot(t,r)
hold on
plot(t,rMoon)
plot(x_int,y_int,'rx')
xlabel('Time (s)')
ylabel('Radius (km)')

function dydt = odefun(t,y)
global A_const;
global B_const;
global C_const;
    dydt = zeros(3,1);
    dydt(1) = y(2);
    dydt(2) = ((y(3)^2)-y(1))/(y(1)^3);
    dydt(3) = (A_const/(B_const - C_const*t))*y(1);
end

[Dyuman Joshi]

Because one of the values in your data is not finite (see below). And interpolation in between infinite set of points is rather un-defined (for the lack of a better word).

%% AEM 588 HW1 Question 2
clear all;
close all;
clc;
global A_const;
global B_const;
global C_const;
mu = 398600; %km^3/s^2
% % nu0 = 1e-3;
Isp = 100;
r0 = 2378 + 12800; %km
m0 = 8; %kg
T = 12/1000;
v0 = sqrt(mu/r0);
rho0 =1;
tau0 = 0;
nu0 = T/m0/9.81;
T0 = nu0*(mu*m0)/r0^2*1000.;
mdot = T0/Isp/9.81;
A_const = T0*r0^2/1000;
B_const = mu*m0;
C_const = mdot*sqrt(mu*r0^3);

tspan = [0 10000];
initialConditions = [1.;0.;1.];

%Solve ODE
[tau,rho] = ode45(@odefun,tspan,initialConditions);
t = tau;
r = rho(:,1);
min(r)

ans = -Inf

rMoonNorm = ones(length(r),1).*(384400/r0);
b_line = polyfit(t,rMoonNorm,1);
y_line2 = polyval(b_line,t);
min(y_line2-r)

ans = -Inf

x_int = interp1((y_line2-r),t,0)

Error using matlab.internal.math.interp1
The sample points must be finite.

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

y_int = polyval(b_line,x_int);

figure(1); clf(1);
plot(t,r)
hold on
plot(t,rMoonNorm)
xlabel('Time, Non-Dimensional')
ylabel('Radius, Non-Dimensional')

t = tau./sqrt(mu/r0^3);
r = rho(:,1).*r0;
rMoon = ones(length(r),1).*384400;
time_intercept = x_int/sqrt(mu/r0^3);
hours_intercept = time_intercept/3600;
days_intercept = hours_intercept/24;
Prop_mass = mdot*time_intercept;
fun = @(x) T0./(m0-mdot*x)
dV = integral(fun,0,time_intercept);

figure(2); clf(2);
plot(t,r)
hold on
plot(t,rMoon)
plot(x_int,y_int,'rx')
xlabel('Time (s)')
ylabel('Radius (km)')

function dydt = odefun(t,y)
global A_const;
global B_const;
global C_const;
    dydt = zeros(3,1);
    dydt(1) = y(2);
    dydt(2) = ((y(3)^2)-y(1))/(y(1)^3);
    dydt(3) = (A_const/(B_const - C_const*t))*y(1);
end

[KSSV]

Check your tspan llimits.....You may reduce it? Also see are all the parameters used are in the same unit system.

Answer 1

[Bhanu Prakash]

Hi Shawn,

As per my understanding, you are trying to interpolate a 1-D function using "interp1" function and are facing some errors in it.

If you look at the code, there is a matrix "r" which is passed as an argument to the "interp1" function. The matrix "r" contains integers values along with "NaN" and "Inf (infinity)" values. These values are the reason for the error.

One workaround for this error is to replace the "NaN" and "Inf" values with finite values. I have tried this at my end and the code worked fine.

Hope this answer helps you.

Thanks,

Bhanu Prakash.