Path: utzoo!attcan!uunet!gill!paul
From: paul@gill.UUCP (Paul Nordstrom)
Newsgroups: comp.lang.c++
Subject: Re: C++ vrs Fortran for linear algebra.
Summary: results for Sun 3/60, OS 4.0.1, Oregon c++
Keywords: matrix
Message-ID: <508@gill.UUCP>
Date: 28 Jul 89 22:18:25 GMT
References: <3967@portia.Stanford.EDU>
Organization: Gill & Co., L.P., San Francisco, CA
Lines: 51

In article <3967@portia.Stanford.EDU>, jon@hanauma (Jon Claerbout) writes:
> 
> ABSTRACT:	C++ can be customized to look like Fortran in its
> 		array subscription, but it has an advantage
> 		over Fortran that variable dimensioned arrays
> 		can be dynamically allocated.
> 		A benchmark shows C++ about half as fast on a DEC 3100.
> 
> ANALYSIS:	fortran			C
> 		real x(n,m)		x = alloc( n*m* sizeof(float))
> 		x(i,j) = etc		x[ i + index[j] ] = etc
> 
> COMMENT:	This is a great example for C++ textbook writers.
> 
> COMPILER:	AT&T C++ version 1.2.1
> 
> DEMONSTRATION BELOW -------------------------------------------------
> /*	Benchmark Fortran equivalent (actually ratfor)


code went here


>//   7.0sec	1575556480. 	DEC 3100  (f77 -O3)
>//  13.1sec	1575559552	DEC 3100  (C++ -O2)
>//

On a sun 3/60 w/ 12 MB and Oregon c++ 1.2Ag

/usr/local/paul % time bench
total=1576677723.402206
    1576677724. if double precision
108.7u 0.3s 1:52 96% 0+12k 5+1io 4pf+0w
/usr/local/paul % !!
time bench
total=1576677723.402206
    1576677724. if double precision
108.8u 0.2s 1:50 98% 0+12k 0+0io 0pf+0w


One thing bothers me though... my results are so accurate I think that
the compiler is using double precision, even though the program 
specifies float.  Havn't found anything relevant in the manual. Obviously
that would explain some of the difference in the timing.  I don't think that
that is the the entire difference, though :-).


-- 
Paul Nordstrom
Gill & Co., L.P.
uunet!gill!paul