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## octave 3.2.4 functions

 From: john Subject: octave 3.2.4 functions Date: Fri, 29 Jul 2011 06:45:16 -0700 (PDT)

```Hi,

I have a problem to run the following programs with functions.It's concern
of solution of a diff.vgl and

eulers method for solving diff.vgl.
function y = rk2a( f, y0, t )
% ----------------------------------------------------------------------
% Gordon College
% March 22, 1999
%
% Usage: y = rk2a(@f, y0, t)
%
% Returns:
%     one-dimensional array of y values associated with the t values
%     passed into the function.
%
% Parameters:
%     f:      handle of function equal to dy/dt.
%     y0:     y value corresponding to t(1), initial t value
%     t:      array of points to evaluate solution at
%
% This function implements a 2nd order Runge-Kutta algorithm to solve the
% initial value problem
%
%     dy
%     -- = f(y,t),     y(t_0) = y_0
%     dt
%
% This particular version is based on the algorithm presented in
"Numerical
% Analysis", 6th Edition, by Burden and Faires, Brooks-Cole, 1997.
% ----------------------------------------------------------------------

[m, n] = size( t );
y = zeros( m, n );
n = max( m, n );

y(1) = y0;

for i = 1 : n-1
h = t(i+1) - t(i);
k1 = h * f( y(i), t(i) ) / 2.0;
y(i+1) = y(i) + h * f( y(i) + k1, t(i) + h / 2.0 );
end

end
How do I run this program,I tried everything but no result.

----_--second program:
function xdot = f (x, t)
r = k = 1.4;
a = 1.5;
b = 0.16;
c = 0.9;
d = 0.8;
xdot(1) = r*x(1)*(1 - x(1)/k) - a*x(1)*x(2)/(1 + b*x(1));
xdot(2) = c*a*x(1)*x(2)/(1 + b*x(1)) - d*x(2);
endfunction
x0 = [1; 2];
t = linspace (0, 50, 200)';
x = lsode ("f", x0, t);
plot (t, x)

When I save this program as "function xdot" and I type function xdot at the
octave prompt
,no result.

I have a problem to save this functions and to run.

How can I save and run this programs????

Can you help me?

Thank you

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