<

Robert Israel

6467 Reputation

21 Badges

15 years, 278 days
University of British Columbia
Associate Professor Emeritus
North York, Ontario, Canada

MaplePrimes Activity


These are replies submitted by Robert Israel

Yes, it would be very handy to have an "unstep" command.  Unfortunately, computers are not time-reversible: there's no way to go back to a previous state, unless you explicitly store that previous state (and storing every state automatically on the chance that you might want to go back there would eat up huge amounts of memory).  What you might be able to do, after seeing where stoperror takes you, is look at the code, set a convenient breakpoint some distance before that location, and then start again.  But it is tricky, especially in a case where the same piece of code is executed successfully 999 times and then produces an error the 1000'th time.

Ah, I think I see what you mean: the light-blue borders and the column on the right containing "Ask a Question", etc. take up so much of the page that some of the text of the posting is lost.

On Firefox's View menu, choose Page Style, and change it from "Basic Page Style" to "No Style".  It won't be as pretty, but you should see the whole posting.

Actually the difference between the indefinite sum and the definite sum from 1 to n is not a constant.  What should be constant is the difference between sum(f(n), n) and sum(f(i),i=1..n-1).

Actually the difference between the indefinite sum and the definite sum from 1 to n is not a constant.  What should be constant is the difference between sum(f(n), n) and sum(f(i),i=1..n-1).

Robert: I think what seanstnn means is this.  A standing wave can be created by the interference of two waves of the same amplitude moving in opposite directions:

> expand(cos(omega*(x-k*t)) + cos(omega*(x+k*t)));

You might try something like this:

> plots:-animate(plot,[cos(x-t)+cos(x+t),x=0..4*Pi],t=0..2*Pi);

Robert: I think what seanstnn means is this.  A standing wave can be created by the interference of two waves of the same amplitude moving in opposite directions:

> expand(cos(omega*(x-k*t)) + cos(omega*(x+k*t)));

You might try something like this:

> plots:-animate(plot,[cos(x-t)+cos(x+t),x=0..4*Pi],t=0..2*Pi);

It might help if we could see the actual system.  You could upload a worksheet file using the green up-arrow button.

@Alejandro Jakubi : actually I have such a script in my Maple Advisor Database:

http://www.math.ubc.ca/~israel/advisor/advisor6/h24r1.htm

 

It might still be made to work.

@Alejandro Jakubi : actually I have such a script in my Maple Advisor Database:

http://www.math.ubc.ca/~israel/advisor/advisor6/h24r1.htm

 

It might still be made to work.

It might depend on the contents of the worksheet.  The safest case is where the worksheet contains no output. 

It might depend on the contents of the worksheet.  The safest case is where the worksheet contains no output. 

@thwle : plottools has its own arrow procedure, which requires more arguments and produces a POLYGONS rather than a PLOT structure.  The POLYGONS must be included in a PLOT.  For example:

> with(plots): with(plottools):
   f:= t -> PLOT(arrow([0,0],[0,cos(t)],.2,.4,.1,colour=green));
   animate(f,[t],t=0..4*Pi,view=[-1..1,-1..1]);

Or you could use the arrow from plots:

> with(plots): with(plottools):
   animate(plots:-arrow, [[0,0],[0,cos(t)]],t=0..4*Pi,view=[-1..1,-1..1]);

@thwle : plottools has its own arrow procedure, which requires more arguments and produces a POLYGONS rather than a PLOT structure.  The POLYGONS must be included in a PLOT.  For example:

> with(plots): with(plottools):
   f:= t -> PLOT(arrow([0,0],[0,cos(t)],.2,.4,.1,colour=green));
   animate(f,[t],t=0..4*Pi,view=[-1..1,-1..1]);

Or you could use the arrow from plots:

> with(plots): with(plottools):
   animate(plots:-arrow, [[0,0],[0,cos(t)]],t=0..4*Pi,view=[-1..1,-1..1]);

Thanks, the "quickly insert first frame" seems to work for me.  It wouldn't have been so bad if the last frame of the old animation was displayed: the problem was that it was going back to the first frame of the old animation.

Thanks, the "quickly insert first frame" seems to work for me.  It wouldn't have been so bad if the last frame of the old animation was displayed: the problem was that it was going back to the first frame of the old animation.

1 2 3 4 5 6 7 Last Page 3 of 187