Dear John
Nice to hear from you. I don't know why DERIVE is unhappy about globally
substituting for theta with pi/2 in your rotation matrix via the SUB icon.
Ironically, you can substitute for theta using the SUB icon on a highlighted
row of the matrix but this is not particularly helpful. Interestingly you
can use DERIVE's SUBST command by entering
SUBST(a,theta,pi/2) where "a" is the rotation matrix and the desired
simplification is then carried out.
Cheers,
Your old mate Boz.
----- Original Message -----
From: "John Hammond" <[log in to unmask]>
To: <[log in to unmask]>
Sent: 22 February 2001 19:55
Subject: Variable substitution in DERIVE 5
> Can someone help, please, with the following?
>
> In DERIVE I set up the matrix for rotation of theta anticlockwise about
the
> origin (in the (x,y)-plane).
>
> If I then try to substitute (Using Simplify_Variable substitution) for the
variable
> theta with the value pi/2 (entering pi either by choosing the symbol pi
from the
> icon-bar, or by entering the word pi) I always get the error message
"Syntax
> error".
>
> If, on the other hand, I highlight the relevant matrix and copy it into
the
> command line (using the function key F3) and change each theta into pi/2
> (either symbol from icon bar, or letters pi) and press <Enter> I get the
correct
> matrix displayed in the Algenbra window with each theta correctly replaced
> by pi/2 (as a symbol). This then correctly evaluates (Using the = to the
left of
> the command line) to the matrix [0 -1; 1 0].
>
> Can someone please explain why DERIVE is giving the syntax error
> message but correctly performing by my alternative method?
>
> How can I get DERIVE to behave properly here?
>
> Ta, in advance.
>
> John.
>
>
> John Hammond
> Mathematics and Statistics Academic Group
> Middlesex University
> Queensway
> Enfield EN3 4SF
> UNITED KINGDOM
>
> Telephone +44 (0)181 362 5392
> Facsimile +44 (0)181 362 6390
>
> E-Mail [log in to unmask]
>
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