“无法从字面上证明'expr` ..."尝试在函数内比较符号时出错 [英] "Unable to prove `expr` literally..." error when trying to compare a symbol inside a function

问题描述

我刚刚开始学习MATLAB，我正试图规范由

给出的bump函数.

I just started learning MATLAB and I'm trying to normalize a bump function given by

function b = bump(x)
region1 = abs(x) < 1
b(region1) = (exp(-1./(1 - x(region1).^2)))
region2 = abs(x) >= 1
b(region2) = 0
end

为此，我需要将定积分从-1除以1.但是，当我输入

To do this, I need to divide by the definite integral from -1 to 1. However, when I input

syms x;
int(bump(x), -1, 1)

我收到一则很长的错误消息，内容为

I get a long error message, which says

使用symengine时出错(第58行)
无法证明'abs(x)<从字面上看是1'.要以数学方式测试该语句，请使用isAlways.

Error using symengine (line 58)
Unable to prove 'abs(x) < 1' literally. To test the statement mathematically, use isAlways.

sym/subsindex错误(第1554行)
X = find(mupadmex('symobj :: logical'，A.s，9))-1;

Error in sym/subsindex (line 1554)
X = find(mupadmex('symobj::logical',A.s,9)) - 1;

sym> privformat中的错误(第2357行)
x = subsindex(x)+1;

Error in sym>privformat (line 2357)
x = subsindex(x)+1;

sym/subsref错误(第1578行)
[inds {k}，refs {k}] = privformat(inds {k});

Error in sym/subsref (line 1578)
[inds{k},refs{k}] = privformat(inds{k});

凹凸错误(第3行)
b(region1)=(exp(-1 ./(1-x(region1).^ 2)))

Error in bump (line 3)
b(region1) = (exp(-1./(1 - x(region1).^2)))

我尝试用我认为的isAlways(abs(x)<1)替换abs(x)<1，尽管它给出了错误的答案(它说积分为零)，但是可以消除错误.

I tried replacing abs(x)<1 with what I think is the suggested isAlways(abs(x)<1), and that removes the error, although it gives the wrong answer (it says the integral is zero).

我不明白错误消息的含义.

I don't understand what does the error message means.

推荐答案

syms x将x定义为符号变量，并在x上调用符号计算.这可能不是您想要的.

syms x defines x as a symbolic variable, invoking symbolic computation on x. This probably isn't what you want.

相反，将x定义为某种输入矩阵，例如x = zeros(3);.或者，要进行数值积分，请使用 integral 函数:

Instead, define x as some kind of input matrix, e.g. x = zeros(3);. Or, to do numeric integration, use the integral function:

integral(@bump, -1, 1)

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