Evaluate function in Matlab

Question

I am trying to evaluate the function in t = 1 in Matlab. How can I get an answer to the following code ?

result = dsolve('D2y-23*Dy+22*y=sin(t)','y(0)=0','Dy(0)=0');
disp(result);
disp(fnval(result, 1));

The first answer is: exp(22*t)/10185 + (23*cos(t))/970 - exp(t)/42 + (21*sin(t))/970.

But when I am trying to find the evaluation of the function in the point t =1, the progrem is throwing some exception. Maybe the 'fnval' function is not suitable for here.

Stewie Griffin · Accepted Answer · 2014-01-05 22:49:11Z

3

You can use subs.

result = dsolve('D2y-23*Dy+22*y=sin(t)','y(0)=0','Dy(0)=0');
t = 1;
subs(result)

ans =   
  3.5198e+005

You could also do it using eval, which is similar to your initial approach:

eval(result)

after assigning a value to t.

You can evaluate the function for a number range, using eval together with vectorize:

t = -0.1:0.01:0.1;
plot(t,eval(vectorize(result)))

This gives:

enter image description here

edited Jan 5, 2014 at 22:49

answered Jan 5, 2014 at 22:37

Stewie Griffin

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