Solve for diff(e2, x, 1) after x and d have been reassigned new values after e4.
Subject: Solve for diff(e2, x, 1) after x and d have been reassigned new values after e4.
From: William Porter
Date: Thu, 29 Jul 2010 10:15:33 -0700
Solve for diff(e2,x,1) after x and d have been reassigned new values after
e4.
I have the following expressions.
(%i1) e1: x^2+d*y*4+d^2*(-4);
2 2
(%o1) 4 d y + x - 4 d
(%i2) e2: solve(e1, y);
2 2
x - 4 d
(%o2) [y = - ---------]
4 d
(%i3) e3: subst([y=0, d=5], e1);
2
(%o3) x - 100
(%i4) e4: solve(e3, x);
(%o4) [x = - 10, x = 10]
(%i5) e5: subst([x=50, d=25], e2);
(%o5) [y = 0]
Now e4 has been reassigned new values at e5, x=50 and d=50. If I write e6:
solve(e5,x); then I get [], which gives me nothing. Because when I continue
to solve and assign as follows.
(%i6) e6: solve(e5,x);
(%o6) []
(%i7) e7: diff(e2,x,1);
x
(%o7) [0 = - ---]
2 d
(%i8) %phi[1] : e7;
x
(%o8) [0 = - ---]
2 d
(%i9) %phi[2] : e7;
x
(%o9) [0 = - ---]
2 d
Now when I execute.
(%i10) subst([e6[1], d=25],%phi[1]);
(%i11) subst([e6[2], d=25],%phi[2]);
I get "Improper index to list or matrix - an error.
The values I should have for (%i10) and (%i11) should be 1.0 and -1.0. The
purpose of this set of expressions is to be able to reassign values to x and
d and wind up with the derivative values of (%i2).
Does anyone have a solution?
William Porter
wporter at omegapar.com