Question

这是我的MATLAB代码。函数trapezoidal（）是单独定义的，它可以正常工作。

syms x;

f = 10 + 2 * x - 6 * (x^2) + 5 * (x^4);

a = 0;
b = 2;

ans_3points = trapezoidal(f, a, b, 3);
ans_5points = trapezoidal(f, a, b, 5);
ans_7points = trapezoidal(f, a, b, 7);

fprintf('Integral estimate for three equally spaced points is %f.\n', ans_3points);
fprintf('Integral estimate for five equally spaced points is %f.\n', ans_5points);
fprintf('Integral estimate for seven equally spaced points is %f.\n', ans_7points);

actual_ans = int(f, 0, 2);

error_3points = 100 * (actual_ans - ans_3points) / actual_ans;
error_5points = 100 * (actual_ans - ans_5points) / actual_ans;
error_7points = 100 * (actual_ans - ans_7points) / actual_ans;

fprintf('Percentage relative error for three equally spaced points is %f.\n', error_3points);
fprintf('Percentage relative error for five equally spaced points is %f.\n', error_5points);
fprintf('Percentage relative error for seven equally spaced points is %f.\n', error_7points);

但是这会在打印error_3points的行中出现以下错误： ???使用==＆gt;时出错fprintf中没有为'sym'输入定义函数。

我没有在fprintf（）中输入任何'sym'输入吗？ ans_3points，ans_5points，ans_7points打印没有任何问题。计算错误但我检查时它们显示为分数。这段代码究竟出现了什么问题？我真的无法弄明白。谢谢。

功能trapezoidal：

function l = trapezoidal(f, a, b, n)

N = n - 1;  % N - the number of segmets

syms x;

series_sum = 0;

for i = (0 : (N - 1))
    series_sum = series_sum + subs(f, x, xterm(i, a, b, n)) + subs(f, x, xterm((i + 1), a, b, n));
end

l = series_sum * (b - a) / (2 * N);

Answer 1

问题在于使用函数int

actual_ans = int(f, 0, 2);

`actual_ans＆＃39;仍然是一个象征性的变量，即使它是一个常数。您可以使用

将其转换为数字变量

actual_ans = double(actual_ans);

使用==＆gt;时出错fprintf函数未定义为＆＃39; sym＆＃39;输入

1 个答案: