## solving symbolic equations with partial derivatives

hello, I can’t find a solution to the following problem: i am trying to solve symbolically some equations which include partial derivatives and a change of reference.

Here is the code:

syms Cf(zf, zr) Cr(zf, zr) theta z L

z = zf;

theta = (zf – zr)/L;

Cf_z = diff(Cf, z);

Cf_f = diff(Cf, zf);

Cf_r = diff(Cf, zr);

Cf_theta = diff(Cf, theta);

eqn = [diff(Cf, z)*diff(z, zf) + diff(Cf, theta)*diff(theta, zf) == diff(Cf, zf), diff(Cf, z)*diff(z, zr) + diff(Cf, theta)*diff(theta, zr) == diff(Cf, zr)];

S= solve(eqn)

when i run this, the following error appears:

"Second argument must be a variable or a nonnegative integer specifying the number of differentiations." (@ line 7) because i doesn’t recognize theta as a variable of Cf. How can i make the change of reference effective so that it can calculate the partial derivatives of Cf in the new reference z, theta?

thank you very muchhello, I can’t find a solution to the following problem: i am trying to solve symbolically some equations which include partial derivatives and a change of reference.

Here is the code:

syms Cf(zf, zr) Cr(zf, zr) theta z L

z = zf;

theta = (zf – zr)/L;

Cf_z = diff(Cf, z);

Cf_f = diff(Cf, zf);

Cf_r = diff(Cf, zr);

Cf_theta = diff(Cf, theta);

eqn = [diff(Cf, z)*diff(z, zf) + diff(Cf, theta)*diff(theta, zf) == diff(Cf, zf), diff(Cf, z)*diff(z, zr) + diff(Cf, theta)*diff(theta, zr) == diff(Cf, zr)];

S= solve(eqn)

when i run this, the following error appears:

"Second argument must be a variable or a nonnegative integer specifying the number of differentiations." (@ line 7) because i doesn’t recognize theta as a variable of Cf. How can i make the change of reference effective so that it can calculate the partial derivatives of Cf in the new reference z, theta?

thank you very much hello, I can’t find a solution to the following problem: i am trying to solve symbolically some equations which include partial derivatives and a change of reference.

Here is the code:

syms Cf(zf, zr) Cr(zf, zr) theta z L

z = zf;

theta = (zf – zr)/L;

Cf_z = diff(Cf, z);

Cf_f = diff(Cf, zf);

Cf_r = diff(Cf, zr);

Cf_theta = diff(Cf, theta);

eqn = [diff(Cf, z)*diff(z, zf) + diff(Cf, theta)*diff(theta, zf) == diff(Cf, zf), diff(Cf, z)*diff(z, zr) + diff(Cf, theta)*diff(theta, zr) == diff(Cf, zr)];

S= solve(eqn)

when i run this, the following error appears:

"Second argument must be a variable or a nonnegative integer specifying the number of differentiations." (@ line 7) because i doesn’t recognize theta as a variable of Cf. How can i make the change of reference effective so that it can calculate the partial derivatives of Cf in the new reference z, theta?

thank you very much symbolic, symbolic math, symbolic math toolbox, derivatives, solve MATLAB Answers — New Questions