如何在Matlab中简化符号和数字混合表达式 [英] How to simplify a symbolic and numeric mixed expression in Matlab

问题描述

我有一个符号和数字混合的表达式:

I have a symbolic and numeric mixed expression:

(3145495418313256125*sin(11334310783410932061962315977/17437937757178560512000000000)*cos(theta))/85568392920039424

其中，theta是符号变量.我想简化此表达式，以便将所有数字及其数学运算结果都更改为两倍.

where theta is a symbolic variable. I want to simplify this expression such that all the numeric numbers and their math operation results are changed to double.

推荐答案

就数据类型而言，您不能混合使用浮点数和符号值.但是，您可以使用可变精度算术，以便以十进制形式表示值.使用 vpa :

In terms of data types, you can't mix floating point and symbolic values. However, you can use variable precision arithmetic so that the values are represented in decimal form. Using vpa:

syms theta
y1 = (3145495418313256125*sin(11334310783410932061962315977/17437937757178560512000000000)*cos(theta))/85568392920039424
y2 = vpa(y1)

返回

y2 =

22.24607614528243677915796931637*cos(theta)

y2的数据类型(class)仍为sym.请参见 digits 函数来调整有效位数.

The data type (class) of y2 is still sym. See the digits function to adjust the number of significant digits.

如果要在实际浮点中工作，则需要将符号表达式转换为函数.您可以使用名称混乱的 matlabFunction :自动执行该过程:

If you want to work in actual floating point you'll need to convert your symbolic expression into a function. You can automate that procedure by using the confusingly-named matlabFunction:

thetafun = matlabFunction(y1)

使用双精度变量返回函数:

which returns a function using double precision variables:

thetafun = 

@(theta)cos(theta).*2.224607614528244e1

然后可以调用匿名函数 thetafun就像任何功能，例如thetafun(0.5).

The anonymous function thetafun can then be called just like any function, e.g., thetafun(0.5).

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