changing variables in syms

If I am working in syms and I say

c= I * (a * I + b * J)

How do I tell matlab that I want I * J = 0 so that it outputs

c = I * (a * I)?

Answer 1

[Sean de Wolski]

subs(c,'J',0)

since J or I has to be zero in the substitution and you want I retained.

[Franco]

neither is zero. Basically Im trying to take the dot product of the 2 unit vectors I and J, so I not J is 0, but I*J =0

[Walter Roberson]

I doubt that would output

c = I * (a * I)

as required by the poster. It would instead output

c = I^2 * a

or

c = a * I^2

It might even output

c = -a

Retaining bracketing in expressions of equal algebraic priority is tricky in symbolic engines, at least without visible constructs such as Mathematica's HOLD .

[Walter Roberson]

Franco, I * J does not express dot product. MuPad expresses dot product via the MuPad routine linalg::scalarProduct (which is not exposed at the MATLAB level.)

If you are using the Maple based symbolic engine, then Maple's dot product operator is . (period), as in maple('A . B')

[Franco]

thanks Walter.