calling a function from a script

Hi all,

I have a differential equation which I want to solve using Euler method.

I created a script which has only the equation:

function dx=differential (t,x);

dx/dt=-x+1/(1+exp(-5*(x-1)));

end

And another script in order to implement Euler's method

f = input('differential.m'); % Enter the function right to the ODE

t0 = input ('Enter initial value of time'); % Value that time starts

x0 = input ('Enter initial value of x'); % Initial condition

tn = input ('End point of time'); % Value that time ends

h = input ('Enter step size'); % TIme step value

% Euler method & Initial conditions

t(1)= t0;

x(1)= x0;

% Euler Loop

for i=1:n

x(i+1) = x(i) + h*f(t(i),x(i));

t(i+1) = t0 + i*h;

end

I want when I press play to the script of Euler's solution, instead of putting the differential equation manually, to call it direclty from the script which includes the equation.

How can I do this, and in which form should the equation be written in order to achieve this?

Thank you very much

Yours sincerely

Ilias Minas

Answer 1

[Geoff Hayes]

@Ilias Minas - can't you just replace f with differential like

t0 = input ('Enter initial value of time'); % Value that time starts
x0 = input ('Enter initial value of x'); % Initial condition
tn = input ('End point of time'); % Value that time ends
h = input ('Enter step size'); % TIme step value
% Euler method & Initial conditions
t(1)= t0;
x(1)= x0;
% Euler Loop
for i=1:n
    x(i+1) = x(i) + h*differential(t(i),x(i));
    t(i+1) = t0 + i*h;
end

[Ilias Minas]

Thank you very much

[Ilias Minas]

Unfortunately is not working. The following error appears

Error: File: differential.m Line: 3 Column: 6

Incorrect use of '=' operator. To assign a value to a variable, use '='. To compare values for equality, use

'=='.

Error in euler_method (line 19)

x(i+1) = x(i) + h*differential(t(i),x(i));

[Voss]

The function 'differential':

function dx=differential (t,x);
    dx/dt=-x+1/(1+exp(-5*(x-1)));
end

contains a syntax error: 'dx/dt' is not a valid expression for assignment

[Torsten]

function dx = differential (t,x);
  dx = -x+1/(1+exp(-5*(x-1)));
end