20070821, 23:01  #1 
Aug 2002
2×7×13×47 Posts 
Formula entry enhancement?
We like how in GMPECM you can tell it to use a formula, instead of having to use the decimal expansion like it used to be.
What we think would be cool is if the program would show the first 3 digits and then the last 3 digits of the number, or some arbitrary number of digits, to verify that the formula is typed in properly. (In our case we use bc to make sure the number is right but we have no idea if what GMPECM is using is right, other than the number of digits listed in the output.) For example, one of the lists we have has the first few digits printed, so you are pretty sure you have the right thing typed in if those digits match. Since we sometimes have to divide out 3 or more huge factors the chance of us typing the number wrong is pretty good, since we can barely type to begin with. So maybe the output would look like this: Code:
GMPECM 6.1.1 [powered by GMP 4.2.1] [ECM] Input number is (12^2291)/841357 (242 digits) (161...843) Using B1=850000000, B2=15892628251516, polynomial Dickson(30), sigma=2176429102 
20070822, 11:59  #2  
Bamboozled!
"๐บ๐๐ท๐ท๐ญ"
May 2003
Down not across
2×3×29×67 Posts 
Quote:
Paul 

20070822, 12:17  #3 
Oct 2004
Austria
4662_{8} Posts 
I agree. And it would be even better if the resulting number is checked if it's an integer:
A typo in one of the (long) factors which are to be divided out before ECMing, the parser cuts off the digits behind the decimal point after the division, and then I wonder why the number is divilible by things like 2^{4}*3*5ยฒ*17 (or even worse, if it is NOT divisible by such small stuff and the first "factor" is e.g. a p37 which looks quite ok, but in fact is nonsense....) Last fiddled with by Andi47 on 20070822 at 12:17 
20070822, 14:20  #4 
"Bob Silverman"
Nov 2003
North of Boston
2^{2}×1,877 Posts 
I disagree. You are putting the onus on the GMP authors to provide
a formula interpreter for (possibly) a very large set of different formulae. Instead, if a particular user has some fomula he wants evaluated, let HIM write the code to evaluate the formula and then have that code call GMPECM with the desired number. Are ALL of the ECM users too lazy to be bothered writing even a little bit of code???? 
20070822, 15:24  #5 
Jun 2003
2^{2}·3^{2}·151 Posts 
The formula interpreter is already there in gmpecm. OP was requesting for a feedback display of the digits so that the user can confirm that the formula was correctly entered.

20070822, 19:54  #6  
Bamboozled!
"๐บ๐๐ท๐ท๐ญ"
May 2003
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2·3·29·67 Posts 
Quote:
Given that the code is there already, an extremely simple validator for its input would appear to be well worth the investment required to write that validator  especially as the code to produce the decimal representation is also present in ECM already. Paul 

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