[GiNaC-devel] pseries patch

[Sheplyakov Alexei]

Hello!

On Mon, Feb 12, 2007 at 12:55:41AM +0000, Vladimir Kisil wrote:
> 		Dear All,
> 
> 		I come across an inability of GiNaC to compute simple series,
>   e.g. in the following example:
> 
> #include <iostream>
> #include <ginac/ginac.h>
> using namespace std;
> using namespace GiNaC;
> 
> int main(){
> 	possymbol t("t");
> 	cout << pow(2-sqrt(1-t), -1).series(t==0,2) << endl;
> 	cout << pow(1-sqrt(1-pow(t,2)), -1).series(t==0,2) << endl;
> }

BTW,

series((1+exp(t), -4), t, 2);

works just fine, because (1+exp(t)).ldegree(t) returns zero. I think
it should throw an exception just like (1+sqrt(t)).ldegree(t) does. 

> Index: ginac/pseries.cpp
> ===================================================================
> RCS file: /home/cvs/GiNaC/ginac/pseries.cpp,v
> retrieving revision 1.90
> diff -u -r1.90 pseries.cpp
> --- ginac/pseries.cpp	31 Jan 2007 22:29:20 -0000	1.90
> +++ ginac/pseries.cpp	12 Feb 2007 01:02:56 -0000
> @@ -1072,7 +1072,11 @@
>  	}
>  	const ex& sym = r.lhs();
>  	// find existing minimal degree
> -	int real_ldegree = basis.expand().ldegree(sym-r.rhs());
> +	int real_ldegree;
> +	try {
> +		real_ldegree = basis.expand().ldegree(sym-r.rhs());
> +	} catch (std::runtime_error) { }

I don't think ignoring such a generic exception is a good idea. It just
hides the bug instead of fixing it. And probably introduces even more
bugs... I propose this patch instead:


[PATCH] power::series: fix failure when basis is not a rational function

Fixes failure to compute series such as (in ginsh notation)

series((1+sqrt(1-t))^(-1), t, 2);
unable to compute series (power::ldegree(): undefined degree because of non-integer exponent)

---
 ginac/pseries.cpp |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/ginac/pseries.cpp b/ginac/pseries.cpp
index db7cef3..ca14c60 100644
--- a/ginac/pseries.cpp
+++ b/ginac/pseries.cpp
@@ -1072,7 +1072,10 @@ ex power::series(const relational & r, int order, unsigned options) const
 	}
 	const ex& sym = r.lhs();
 	// find existing minimal degree
-	int real_ldegree = basis.expand().ldegree(sym-r.rhs());
+	ex eb = basis.expand();
+	int real_ldegree = 0;
+	if (eb.info(rational_function))
+		real_ldegree = eb.ldegree(sym-r.rhs());
 	if (real_ldegree == 0) {
 		int orderloop = 0;
 		do {
-- 
1.4.4.4


Best regards,
 Alexei

-- 
All science is either physics or stamp collecting.

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