我用matlab算了一下，最后一行数据不一样。
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3799248216530963946104908731687 718950889 7# mathe
我用matlab算了一下，最后一行数据不一样。
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。。。
3799248216530963946104908731687 718950889
G-Spider 发表于 2011-1-13 19:30 http://bbs.emath.ac.cn/images/common/back.gif
用matlab算，怎样才能得到如此高的精度？（我也用matlab算，好像精度不够） 12# sheng_jianguo
>>help vpa
VPA Variable precision arithmetic.
R = VPA(S) numerically evaluates each element of the double matrix
S using variable precision floating point arithmetic with D decimal
digit accuracy, where D is the current setting of DIGITS.
The resulting R is a SYM.
VPA(S,D) uses D digits, instead of the current setting of DIGITS.
D is an integer or the SYM representation of a number.
It is important to avoid the evaluation of an expression using double
precision floating point arithmetic before it is passed to VPA.
For example,
phi = vpa((1+sqrt(5))/2)
first computes a 16-digit approximation to the golden ratio, then
converts that approximation to one with d digits, where d is the current
setting of DIGITS.To get full precision, use unevaluated string or
symbolic arguments,
phi = vpa('(1+sqrt(5))/2')
or
s = sym('sqrt(5)')
phi = vpa((1+s)/2);
//////////////////////////
可见matlab有良好的大数运算功能。
vpa('173746*sin(10^22)+94228*log(17.1)-78487*exp(0.42)',1000)%注意要加上引号，不然每一项不到15位的精度，最后的结果比1000的精度略低一点，存在舍入 13# G-Spider
谢谢！ :b:我是打酱油的，
过来看看各位老大。 9# wayne
代码不好，在windows的MinGW下编译，即使开了-Wall也不警告，运行也很正常。
在linux下编译没问题，但运行时会出现segmentation fault .
检查了很长时间，原来是argv 使然。
现在更正如下： #include <stdio.h>
#include <stdlib.h>
#include <mpfr.h>
int main (int argc, char *argv[])
{int m;
if (argc>1) m= atoi(argv)-1;
else printf("usage: %s n\n",argv),exit(1);
mp_prec_t p = 100+5*m;
mpfr_t a, b, c, d;
mpfr_inits2 (p, a, b, c, d, (mpfr_ptr) 0);
mpfr_set_str (a, "1e22", 10, GMP_RNDN);
mpfr_sin (a, a, GMP_RNDN);
mpfr_mul_ui (a, a, 173746, GMP_RNDN);
mpfr_set_str (b, "17.1", 10, GMP_RNDN);
mpfr_log (b, b, GMP_RNDN);
mpfr_mul_ui (b, b, 94228, GMP_RNDN);
mpfr_set_str (c, "0.42", 10, GMP_RNDN);
mpfr_exp (c, c, GMP_RNDN);
mpfr_mul_si (c, c, -78487, GMP_RNDN);
mpfr_add (d, a, b, GMP_RNDN);
mpfr_add (d, d, c, GMP_RNDN);
mpfr_printf ("d=%.*Re\n",m,d);
mpfr_clears (a, b, c, d, NULL);
return 0;
}
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