MaplePrimes - comments on Post, Possible bugs in Maple 14 (Evalf command and more)

MaplePrimes - comments on Post, Possible bugs in Maple 14 (Evalf command and more) http://www.mapleprimes.com/posts/96064-Possible-Bugs-In-Maple-14-Evalf-Command-And-More en-us 2026 Maplesoft, A Division of Waterloo Maple Inc. Maplesoft Document System Fri, 12 Jun 2026 19:48:57 GMT Fri, 12 Jun 2026 19:48:57 GMT The latest comments added to the Post, Possible bugs in Maple 14 (Evalf command and more) http://www.mapleprimes.com/images/mapleprimeswhite.jpg MaplePrimes - comments on Post, Possible bugs in Maple 14 (Evalf command and more) http://www.mapleprimes.com/posts/96064-Possible-Bugs-In-Maple-14-Evalf-Command-And-More quote it http://www.mapleprimes.com/posts/96064-Possible-Bugs-In-Maple-14-Evalf-Command-And-More?ref=Feed:MaplePrimes:Possible bugs in Maple 14 (Evalf command and more):Comments#comment96065 Quote the m using single-right quotes in the pop-up, when doing that Units->Replace Units context-menu action. You previously assigned to the global name m. So if you want to use it elsewhere as a unit name, then you have to use so-called uneval quotes (single right-quotes. Otherwise it will get evaluated to whatever you previously assigned to it. Eg, 'm'   As for the evalf question, things tend to break down when Digits is set to less than 4 or 5. We can investigate your example as a simple "atomic" operation -- a multiplication of e1 and e2 which are two floats. At very low Digits the computed result is not accurate to less than an ulp (let alone less than 1/2 an ulp). <pre>> restart: > e1:=evalf[20](Pi): > e2:=evalf[20](4*(1391000/2)^2): > T2:=evalf[20](e1*e2): > for d from 1 to 10 do > forget(evalf); > T1:=evalf[d](e1*e2); > print([testfloat(T1,T2,1,test=1,digits=d)]); > end do: [true] [[false, 2., ulps ]] [[false, 2., ulps ]] [true] [true] [true] [true] [true] [true] [true] </pre> A lesson here is that evalf[d] isn't so useful for very small d (<5). If you want merely to get a shorter form of a floating-point coefficient of a final result then you could either apply evalf[2] to (only) the final value or use the elision settings in the Standard GUI to modify displayed floating-point values automatically (see Options->Precision from the toolbar). The latest comments added to the Post, Possible bugs in Maple 14 (Evalf command and more) 96065 Tue, 17 Aug 2010 19:43:39 Z pagan pagan Also in 12 http://www.mapleprimes.com/posts/96064-Possible-Bugs-In-Maple-14-Evalf-Command-And-More?ref=Feed:MaplePrimes:Possible bugs in Maple 14 (Evalf command and more):Comments#comment96066 hmmmm..... for i from 1 to 4 do    evalf[i](S) end do;         6. 1012         5.9 1012             6.06 1012         6.080 1012 That is an odd one. The latest comments added to the Post, Possible bugs in Maple 14 (Evalf command and more) 96066 Tue, 17 Aug 2010 20:14:57 Z Christopher2222 Christopher2222 Units versus variables http://www.mapleprimes.com/posts/96064-Possible-Bugs-In-Maple-14-Evalf-Command-And-More?ref=Feed:MaplePrimes:Possible bugs in Maple 14 (Evalf command and more):Comments#comment96067 OK, thank you! This makes it work indeed. But then it was a bad suggestion Maple posed in the dialog: kg/m^3. It should have been kg/'m'^3. But maybe it is too much to ask for that Maple should keep track of the variables already defined? I had hoped though that Units and variables did not interfere. I mean units are put in double brackets and should not be mistaken with variables. But obviously that is not the case! Erik   The latest comments added to the Post, Possible bugs in Maple 14 (Evalf command and more) 96067 Tue, 17 Aug 2010 20:22:04 Z erik10 erik10 Evalf then of limited value ... http://www.mapleprimes.com/posts/96064-Possible-Bugs-In-Maple-14-Evalf-Command-And-More?ref=Feed:MaplePrimes:Possible bugs in Maple 14 (Evalf command and more):Comments#comment96068 I understand the problem now: Maple is rounding off to two digits of the individual factors, then make the computation and is rounding off again. This is kind of disappointing. I had expected Maple to calculate the parentheses with full precision and only round off to two digits in the end. As it seem to be now, the evalf command is of limited value to me. Now I can't save command lines: I need to calculate first and then add a new command line in the end to force Maple to do it the way I want.  Why has Maple implemented the evalf command in this way? I don't see any value in that choice? Probably there is a reason, though :) pagan: Shouldn't you divide your evalf computation in even more parts? I mean 4*(1391000/2)^2 could be divided as well. Thank you for all your replies. I appreciate it! Erik  The latest comments added to the Post, Possible bugs in Maple 14 (Evalf command and more) 96068 Tue, 17 Aug 2010 21:14:07 Z erik10 erik10 faq http://www.mapleprimes.com/posts/96064-Possible-Bugs-In-Maple-14-Evalf-Command-And-More?ref=Feed:MaplePrimes:Possible bugs in Maple 14 (Evalf command and more):Comments#comment96069 Okay I found a faq that answers your question, where you came to the same reasoning.  <a href="http://www.maplesoft.com/support/faqs/detail.aspx?sid=87674&pid=1">http://www.maplesoft.com/support/faqs/detail.aspx?sid=87674&pid=1</a> heading : The evalf command is not rounding the answer correctly. I wonder if the intention was to speed up calculations?  To avoid rounding errors like this, in hindsight, I wonder if they could have added a couple of decimal places internally so the number is rounded properly.  However there is probably a few situations that would still bring up this rounding issue.  The latest comments added to the Post, Possible bugs in Maple 14 (Evalf command and more) 96069 Tue, 17 Aug 2010 22:31:13 Z Christopher2222 Christopher2222 Don't forget Maple allows for arbitrary precision http://www.mapleprimes.com/posts/96064-Possible-Bugs-In-Maple-14-Evalf-Command-And-More?ref=Feed:MaplePrimes:Possible bugs in Maple 14 (Evalf command and more):Comments#comment96071 <a href="http://www.mapleprimes.com/posts/96064-Possible-Bugs-In-Maple-14-Evalf-Command-And-More#comment96068">@erik10</a> In Maple, evalf is much more than a rounding function.  evalf[n](x) evaluates x using n digits of precision.    This is particularly useful when you increase n above the default of 10.  You can numerically evaluate the expression using 20, 50 or 1000 digits of precision.  In some sense, there is no "full precision" when using evalf, especially if your calculations include constants like Pi.  Try calling evalf[n](Pi) for various values of n, I think you'll begin to understand why evalf works the way it does. You can evaluate your expression using evalf to compute the result, then call evalf[2] on the result to reduce it to 2 digits of precision. Darin The latest comments added to the Post, Possible bugs in Maple 14 (Evalf command and more) 96071 Tue, 17 Aug 2010 22:48:39 Z dohashi dohashi