Matlab function to calculate

Question

How can I input the two functions from this task in matlab ?
A voltage peak in a circuit is caused by a current through a resistor.
enter image description here

The energy E which is dissipated by the resistor is:
enter image description here
Calculate E if

This is my final solution:

function E = calculateE(i0,R,t0)
syms t;
f = i0*exp(-t/t0) * sin(2*t/t0);
E = int(R*f*f,0,inf);
end

Question: how can I input the above functions in matlab to calculate the result?

yes, but I probably don't want to use the final formula.. but do it all in matlab — Iulian Rosca, May 16 '14 at 16:27
MATLAB is not well-suited for symbolic computation unless you use the symbolic toolbox, but even then this is not a very good problem for that. It is still completely unclear whether you want MATLAB to be computing the integral or what. What are your inputs/outputs? — Emily, May 16 '14 at 16:28
the inputs are i0, R, and t0.. and I want to calculate E , integral of the function — Iulian Rosca, May 16 '14 at 16:30
So if $I_0=100$, $t_0=0.01$, $R=0.5$, you want to compute $100^20.010.5/5$? What is the problem computing that exactly? — hejseb, May 16 '14 at 16:33
actually the solution is irelevant , how can I input the functions i(t) and the integral in matlab? — Iulian Rosca, May 16 '14 at 17:01
You either need to use the symbolic toolbox or choose a numerical quadrature routine. There is no built-in function for generalized integration in MATLAB. — Emily, May 16 '14 at 17:10

score 0 · Answer 1 · answered Feb 02 '15 at 02:56

Forgive me if I am misunderstanding your question. Put that function code in a file named calculateE.m in the directory that you are running MATLAB in. On the MATLAB command line, or in another MATLAB function file, the line myE = calculateE( myi0, myR, myt0); will call the function using values myi0, myR, myt0 and return the result myE.

Carser · Answer 2 · 2014-05-16T17:36:42.100

0

You can write a MATLAB function like

function E = calculateE(i0,R,t0)
  % The function i(t) 
  function y = i(t)
    y = i0 .* exp(-t/t0) .* sin(2.*t/t0); 
  end  

  function y = intFunction(t)
    y = R * i(t).^2;
  end

  % Calculate energy 
  E = integral(@intFunction,0,Inf);
end

edited May 16 '14 at 17:36

answered May 16 '14 at 17:23

Carser

3,400

Undefined function or method 'integral' for input arguments of type 'function_handle'. And you missed R and i^2(t) in calculation of E – Iulian Rosca May 16 '14 at 17:31
@IulianRosca, what version of MATLAB are you using? – Carser May 16 '14 at 17:31
Matlab : 7.12.0.635 – Iulian Rosca May 16 '14 at 17:33
I am using 8.1.0. "integral" must not be available in your older version, so you'll have to do the integration yourself. – Carser May 16 '14 at 17:34
int doesn't work either... – Iulian Rosca May 16 '14 at 17:35
No, int is not a MATLAB function. – Carser May 16 '14 at 17:36
there is actualy a int function – Iulian Rosca May 16 '14 at 17:37
No, there are integer types, but the "int" function you're referring to is probably the MuPAD function (not MATLAB). – Carser May 16 '14 at 17:40
help int --- help for char/int ---
INT Alternative entry to the symbolic integration function. INT(F,...) is the same as int(sym(F),...).
– Iulian Rosca May 16 '14 at 17:41
@IulianRosca, yes you are right. Maybe you can use this function. – Carser May 16 '14 at 17:45
but it still doesn't accept a function_handle – Iulian Rosca May 16 '14 at 17:49
1

Consider upgrading your MATLAB. Or use Octave which has functions such as "quad" – Carser May 16 '14 at 17:56

Matlab function to calculate

2 Answers2