Date: Sun, 3 Mar 2002 18:35:38 -0600 (CST)
From: jr <organism>
Subject: Re: hw proj 4 now

> hello again, you probably won't take a look at this until monday anyway; but 
> just in case...
> 
> i'm getting some very strange error messages when trying to dsolve our eqn 
> for proj4; it says the initial conditions are invalid. i can't see any error 
> in my syntax; could you please point me in the right direction?
> 
> >ode:= diff(y(t), t$2) - diff(y(t), t) +2*y(t);
> 
> 
>                 ode := y``(t) -  y`(t) + 2 y(t) (<- i changed the formatting 
> here to make it easy for you to read...)
> 
> 
> >s:= dsolve({ode = 0, diff(y(0), t) = 1, y(0) = 0},y(t), 'type=series');
                        ^^^^^^^^^^^^^^^^^
I think your problem is with "diff".  I think you want to use "D(y)(0)=1" 
here.  If you're interested in the differences in the sematics, see the 
help files (follow "Mathematics," "Calculus," and "Differential Calculus," 
then see "D," "diff," and "D vs. Diff").

You'll also want to look at the examples in "Mathematics," "Differential 
Equations," "dsolve," and "Initial Conditions."  I might also suggest that 
when defining the ODE, you also specify the right-hand side (and not just 
the LHS).  That is, try:

myode:= diff(y(t), t$2) - diff(y(t), t) +2*y(t) = 0;

or, breaking it into pieces:

myLHS := diff(y(t), t$2) - diff(y(t), t) +2*y(t);
myRHS := sin(t);     <-- or 0 or whatever your heart desires
myode := myLHS = myRHS;

> Error, (in dsolve/process_input) invalid initial condition
> 
> >
> i want to plot it next, & it complained about having too many args when i 
> changed it to "type=numeric'...i find any help at all on this topic.
> 
> all i can come up with is a big "?". thanks for your help; you rock!

This probably stems from the same problem.  Let me know if you have any 
luck!

j