如何在不获取inf的情况下在matlab中计算指数? [英] How to compute an exponent in matlab without getting inf?

问题描述

标题说明了一切:我想用大数字在matlab中计算一个指数，但是我溢出了，它只返回无穷大.

The title says it all: I want to calculate an exponent in matlab with big numbers, but I get overflow and it just returns infinity.

>> 100^1000

ans =

   Inf

我上次检查时，100 ^ 1000绝对小于无穷大:)

Last time I checked, 100^1000 is decidedly smaller than infinity :)

推荐答案

正如丹尼尔(Daniel)所指出的那样，它太大了，甚至无法由MATLAB本身输出.此数字是通过 realmax 获得的，用于不同的数据类型.作为表示/使用如此大的数字的替代方法，您可以将相应的mantissa和exponent与base-10 representation一起使用，这是通常的MATLAB表示形式.这里列出了获得这两个功能的函数-

As Daniel has already pointed out, it's too big a number to be even outputted by MATLAB itself. This number is obtained with realmax for different datatypes. As an alternative to represent/use such huge numbers, you can use the corresponding mantissa and exponent with base-10 representation instead, which is the usual MATLAB representation. The function to get those two is listed here -

function [mantissa, base10_exponent] = base10_mantissa_exponent(base,exponent)

act_exp = exponent*log10(abs(base));
base10_exponent = floor(act_exp);
mantissa = power(10,act_exp - base10_exponent);

if rem(exponent,2)==1 && sign(base)==-1
    mantissa = -mantissa;
end

return;

下面列出了一些示例运行，并与实际的MATLAB运行进行了比较以进行验证.

Few example runs and comparisons with actual MATLAB runs for validation are listed next.

Ex#1

base = -125.343;
exponent = 101;
usual_approach = base^exponent
[mantissa, base10_exponent] = base10_mantissa_exponent(base,exponent)

输出-

usual_approach =
 -8.0930e+211
mantissa =
   -8.0930
base10_exponent =
   211

Ex#2(问题中讨论的问题)

base = 100;
exponent = 1000;

输出-

usual_approach =
   Inf
mantissa =
     1
base10_exponent =
        2000

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