why do i get Nan as output?

im trying to solve four such equations using an input vector containing 4 values.

fn = 1/(rho(1)*Y(1))*(1.113-2.14*Y(1)+2.81*Y(1)^2-1.76*Y(1)^3+0.396*Y(1)^4+0.08694*Y(1)^5-0.0579*Y(1)^6 +0.0077*Y(1)^7);

using ode45.

But the output vector consists of Nan values ; where as its returining numerical values on using the command window.

function file:

function fn = plume5(t,Y)
global rho cp   
 fn(1) = 1/(rho(1)*cp)*(760.91-1608.08*Y(1)+2449.22*Y(1)^2-2001.61*Y(1)^3+904.51*Y(1)^4-212.087*Y(1)^5+20.095*Y(1)^6);
 fn(2) = 1/(rho(2)*cp)*(760.91-1608.08*Y(2)+2449.22*Y(2)^2-2001.61*Y(2)^3+904.51*Y(2)^4-212.087*Y(2)^5+20.095*Y(2)^6);
 fn(3) = 1/(rho(3)*cp)*(760.91-1608.08*Y(3)+2449.22*Y(3)^2-2001.61*Y(3)^3+904.51*Y(3)^4-212.087*Y(3)^5+20.095*Y(3)^6);
 fn(4) = 1/(rho(4)*cp)*(760.91-1608.08*Y(4)+2449.22*Y(4)^2-2001.61*Y(4)^3+904.51*Y(4)^4-212.087*Y(4)^5+20.095*Y(4)^6);
 fn(5) = 1/(rho(5)*Y(5))*(1.113-2.14*Y(5)+2.81*Y(5)^2-1.76*Y(5)^3+0.396*Y(5)^4+0.08694*Y(5)^5-0.0579*Y(5)^6 +0.0077*Y(5)^7);
 fn(6) = 1/(rho(6)*Y(6))*(1.113-2.14*Y(6)+2.81*Y(6)^2-1.76*Y(6)^3+0.396*Y(6)^4+0.08694*Y(6)^5-0.0579*Y(6)^6 +0.0077*Y(6)^7);
 fn(7) = 1/(rho(7)*Y(7))*(1.113-2.14*Y(7)+2.81*Y(7)^2-1.76*Y(7)^3+0.396*Y(7)^4+0.08694*Y(7)^5-0.0579*Y(7)^6 +0.0077*Y(7)^7);
 fn(8) = 1/(rho(8)*Y(8))*(1.113-2.14*Y(8)+2.81*Y(8)^2-1.76*Y(8)^3+0.396*Y(8)^4+0.08694*Y(8)^5-0.0579*Y(8)^6 +0.0077*Y(8)^7);
 fn = fn';

main file

clear all
close all
global rho cp   
rho = [0.4878;0.7862;1.1449;1.1611;0.4878;0.7862;1.1449;1.1611]
cp = 1.4857
t_span= 0:10
y = [0.0182;0.3105;1.2882;2.7341;0.0182;0.3105;1.2882;2.7341]
[A,P]= ode45('plume5',t_span,y);

[Jan]

Notes: Providing the function to be integrated as CHAR vector is outdated for almost 20 years now. Although it works for reasons of backward compatibility, prefer the "modern" method of function handles.

See Answers: Anonymous for params for using anonymous function to provide parameters. This is much better than using global variables:

rho = [0.4878;0.7862;1.1449;1.1611;0.4878;0.7862;1.1449;1.1611];
cp  = 1.4857;
[A,P]= ode45(@(t, Y) plume5(t, Y, roh, cp), t_span, y);

function fn = plume5(t,Y, roh, cp)
...
end

[Sunetra CV]

Thank You

Answer 1

[Jan]

Use te debugger to determine the first occurrence of a NaN. Type this in the command window:

dbstop if naninf

Then run the code again. When Matlab stops, check the value of the trajectory. Most likely there is a pole and NaN or Inf is the correct numerical value. You can check this by:

plot(t, Y)

By the way, vectorization can simplify the code:

function fn = plume5(t,Y, rho, cp)
fn = zeros(8, 1);
fn(1:4) = 1 ./ (rho(1:4)*cp) .* (760.91 - 1608.08 * Y(1:4) + ...
          2449.22 * Y(1:4) .^ 2 - 2001.61 * Y(1:4) .^ 3 + ...
          904.51 * Y(1:4) .^ 4 - 212.087 * Y(1:4) .^ 5 + 20.095 * Y(1:4) .^6 );
fn(5:6) = 1 ./ (rho(5:8) .* Y(5:8)) * (1.113 - 2.14 * Y(5:8) + ...
          2.81 * Y(5:8) .^ 2 - 1.76 * Y(5:8) .^ 3 + 0.396 * Y(5:8) .^ 4 + ...
          0.08694 * Y(5:8) .^ 5 - 0.0579 * Y(5:8) .^ 6 + 0.0077 * Y(5:8) .^ 7);

[Sunetra CV]

The function returned numerical values on reducing the time span to about 0.01 , will scaling down the equation help?

[Moumita Ghosh]

While I run a simulink model in MATLAB, I get an error saying "dbOK does not exist" under "model error" heading..it said either Nan or inf value is taken at the input of model..Can you please help to resolve it?

[Jan]

@Sunetra CV: I'm not sure what "scaling down" means here.

@Moumita Ghosh: I cannot follow you. Your comment does not concern the question of this thread, does it? Then please open a new thread and post the details there.

[Sunetra CV]

As in making the coefficients of y(i) in both the equations of the same range.