problem with subs

David Doria — Mon, 25 Feb 2008 22:08:05 -0500

I make a big 4x4 matrix of second partials:

------

syms A N sigma omega phi x t positive
lnf = -N/2 * log(2*pi*sigma) + -1/(2*sigma)*(x -
A*cos(omega*t - phi));
F=[diff(diff(lnf,A),A) diff(diff(lnf,A),omega)
diff(diff(lnf,A),phi) diff(diff(lnf,A),sigma);
diff(diff(lnf,omega),A) diff(diff(lnf,omega),omega)
diff(diff(lnf,omega),phi) diff(diff(lnf,omega),sigma);
diff(diff(lnf,phi),A) diff(diff(lnf,phi),omega)
diff(diff(lnf,phi),phi) diff(diff(lnf,phi),sigma);
diff(diff(lnf,sigma),A) diff(diff(lnf,sigma),omega)
diff(diff(lnf,sigma),phi) diff(diff(lnf,sigma),sigma)];

----------

Then I want to substitute some values:
subs(F, {A,omega, phi, sigma}, {1, 1, 1, 1})

it doesn't work.

I tried
subs(F(1,2), {A,omega, phi, sigma}, {1, 1, 1, 1})

still no success.

However, if I do F(1,2) then manually copy and paste:
subs(1/2/sigma*sin(-omega*t+phi)*t, {A,omega, phi, sigma},
{1, 1, 1, 1})

it works properly.

Is there a way to do this automatically?

Thanks,

Dave

Re: problem with subs

David Doria — Tue, 26 Feb 2008 12:25:04 -0500

is this not a normal thing to need to do?

Thanks,
Dave
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