## 296 Reputation

18 years, 270 days

## How do I deal with a chimera?...

Frequently a variable appears in an expression but not in the result, e.g., there is no x in int(sin(x),x=0..3). How do I tell that to Maple? I am trying to solve (numerically) an ODE of the form
x^2 y'' + alpha(x) y' +   beta(y) = 0. However, alpha(x) has an integral in its defintion whose upper limit is x. Maple demands that I list the dummy variable of the integral as a parameter. How do I deal with that? BTW, Maple has no problem with plot (alpha(x), x=0..6) for example.

Maple 2015

I have 2 questions.

1) The help pages discuss the use of functions described by piecewise when using dsolve. The examples are clear enough but nothing is said about using the numeric option and piecewise. I get an error message for a very simple example: y' +R(t) y^2 = 0. Are I correct in assuming that dsllve numeric cannot deal with piecwise continuous functions?

2) I tried to solve a system of 2 second order constant coefficient linear ODEs using dsolve. After a very long wait (over an hour) I gave up. I tried again using "method=laplace" and got an instant answer. I did not bother to mention it here but it occurred again, this time with a fourth order and second order constant coefficient system. Very strange! I know that the laplace transform is a very useful tool; shouldn't Maple also know that?

## Can I take a quick peek?...

I  often find mself in the following quandry: I am investigating a problem, I do a few examples, run a do loop for j from1 to 5 to see if that works and then enter

for j from 1 to 200 do  a[j]:=blah, blah,...  end do:

and 15 minutes later nothing has happened. Is the loop finishing up with j = 198 or so or is it stuck at j = 23 and it will take forever to finish? Or perhaps there is an error that turns up for j > 23?

When I think about it I can insert a print(j) command to keep track of this but there are other situations where that doesn't work. For example,

Order := 35; mtaylor(....

When nothing happens is that because the calculation is almost done? or stuck? etc.

Is it possible to take a quick peek at the state of Maple and the decide whtether to continue the computation or abort? If the calculation of mtaylor(... is particularly long I might settle for the 15 coeficients computed so far rather than abort. Can I get at those?

## dealing with errors...

Maple

Hi,

I want (Maple) to do a series of time consuming computations while I sleep so I create a Vector V of length 50 say and make each computation an entry in V.

An occasional entry will turn out to be an error-that is, I get an error message and the calculations stop. Not a serious problem if the first 47 entries have been calculated but if the thrd calcuation fails I have little to show for a night's work.

What I want if for Maple to skip any computaion that fails (produce the appropriate  error message if possible) and then continue with the other computations.  Any suggestions?

Here is an unrelated question. If I have an Array T say
>T:=Array(3..5,7..17,(i,j)->i^2*j):

then T[4,10] returns the appropriate entry. T(2,4) returns the same thing. What type of object is T(-,-)?