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文字

在头文件<math.h>中定义



float expm1f(float arg);

(1)

(自C99以来)

double expm1(double arg);

(2)

(自C99以来)

long double expm1l(long double arg);

(3)

(自C99以来)

在头文件<tgmath.h>中定义



#define expm1(arg)

(4)

(自C99以来)

1-3)计算提升到给定倍率参数的e(欧拉数,2.7182818)减去1.0。 如果arg接近零,则此函数比表达式std :: exp(arg)-1.0更准确。

4)类型 - 通用宏:如果arg的类型是long double,则调用expm1l。 否则,如果arg具有整数类型或类型double,则调用expm1。 否则,调用expm1f。

参数

arg

-

floating point value

返回值

如果没有错误发生 earg

则返回-1。

如果发生由溢出引起的范围错误,则返回+ HUGE_VAL,+ HUGE_VALF或+ HUGE_VALL。

如果由于下溢而发生范围错误,则返回正确的结果(舍入后)。

错误处理

按照math_errhandling中的指定报告错误。

如果实现支持IEEE浮点运算(IEC 60559),

  • 如果参数为±0,则返回,未修改

  • 如果参数是-∞,则返回-1

  • 如果参数是+∞,则返回+∞

  • 如果参数是NaN,则返回NaN

注意

函数expm1和log1p对于财务计算很有用,例如,在计算小的每日利率时:(1 + x)n

-1可以表示为expm1(n * log1p(x))。 这些功能还简化了写入准确的反双曲函数。

对于兼容IEEE的类型,如果709.8 <arg,则保证溢出。

#include <stdio.h>#include <math.h>#include <float.h>#include <errno.h>#include <fenv.h>#pragma STDC FENV_ACCESS ON
int main(void){    printf("expm1(1) = %f\n", expm1(1));    printf("Interest earned in 2 days on $100, compounded daily at 1%%\n"           " on a 30/360 calendar = %f\n",           100*expm1(2*log1p(0.01/360)));    printf("exp(1e-16)-1 = %g, but expm1(1e-16) = %g\n",           exp(1e-16)-1, expm1(1e-16));    // special values    printf("expm1(-0) = %f\n", expm1(-0.0));    printf("expm1(-Inf) = %f\n", expm1(-INFINITY));    //error handling
    errno = 0; feclearexcept(FE_ALL_EXCEPT);    printf("expm1(710) = %f\n", expm1(710));    if(errno == ERANGE) perror("    errno == ERANGE");    if(fetestexcept(FE_OVERFLOW)) puts("    FE_OVERFLOW raised");}

可能的输出:

expm1(1) = 1.718282Interest earned in 2 days on $100, compounded daily at 1%
 on a 30/360 calendar = 0.005556exp(1e-16)-1 = 0, but expm1(1e-16) = 1e-16expm1(-0) = -0.000000expm1(-Inf) = -1.000000expm1(710) = inf
    errno == ERANGE: Result too large
    FE_OVERFLOW raised

参考

  • C11标准(ISO / IEC 9899:2011):

    • 7.12.6.3 expm1函数(p:243)

    • 7.25类型通用数学<tgmath.h>(p:373-375)

    • F.10.3.3 expm1函数(p:521)

  • C99标准(ISO / IEC 9899:1999):

    • 7.12.6.3 expm1函数(p:223-224)

    • 7.22类型通用数学<tgmath.h>(p:335-337)

    • F.9.3.3 expm1函数(p:458)

扩展内容

Expexpfexpl(C99)(C99)

计算e给定的倍率(ex)(函数)

exp2exp2fexp2l(C99)(C99)(C99)

计算2提高到给定的倍率(2x)(功能)

log1plog1pflog1pl(C99)(C99)(C99)

计算1加上给定数(ln(1 + x))(函数)的自然(基e)对数,

| expm1的C ++文档 |

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