MATLAB: How to say that a constant is not a variable

constantdifferential equationsodesymbolic

Hi,

I would like to solve an ode in a analytic way

So i do:

df= @(,) ...
syms T(t)
df1=sym(df);
y0=10 % a constant
f_exact = matlabFunction(dsolve(diff(T,1) == df1 , T(0)== y0));

If I run that i am getting f_exact=@(t,y0) … % function of t and y0

How wan i do to say that y0 is a constant

Thank you

Best Answer

When you do

df = @(t,T) -0.1*(T -10);

then the T is taken from the second argument of df, not from the syms T(t). When you sym(df) then the T that appears in the result is a different T, not the same one as syms T(t) .

Instead of using

df1 = sym(df)

you should be using

syms T(t)
df1 = df(t,T)

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YOu can write first,second and third derivative like below:

df = diff(f,t) ;   %f'
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Check below option also:

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diff(f) would invoke f with no arguments, fetch its return value, and apply the numeric diff() function to it, where the numeric diff() function is (X(2:end) - X(1:end-1)).

If you have the symbolic toolbox, you could try

syms t
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f1 = inline(char(f(t)));
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Or more directly,

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f2 = diff(df, t);
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df2 = matlabFunction(f2, 'vars', t);
f

Best Answer

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