Question

我正在编写一个C ++代码，该代码使用Gauss-Seidel方法来求解方程组（但你不应该知道这是什么来回答我的问题）。这主要涉及用户将一系列值输入到2D阵列中。我的问题发生在值为sin（45）之类的东西时，或者更确切地说是3.14,2.120947或3之类的任何数字等等......这里是代码主循环的片段

/* code to solve an nxn system using the Gauss-Seidel method  */

int i, j, n;
int violation_counter, answer;
int violation_rows[MAX_DIM];
double sum;
double a[MAX_DIM][MAX_DIM];
double b[MAX_DIM],x[MAX_DIM];
/* read in data */
n = MAX_DIM + 1;
while (n > MAX_DIM)
{
    cout << "Enter the dimension of the system to be solved: " << endl;
    cin >> n;
}

/*THIS BLOCK IS WHAT WE'RE CONCERNED WITH*/
cout << endl;
for (i = 0; i < n; i++)
{
    for (j = 0; j < n; j++)
    {
        printf("Enter a[%d][%d] of the system matrix: ", i, j);
        cin >> a[i][j];
    }
    printf("Enter b[%d] of the right-hand-side vector: ", i);
    cin >> b[i];
    cout << endl;
}

/*THE REST OF THE CODE IS FINE I THINK*/

/* test the convergence criterion */
violation_counter = 0;
for (i = 0; i < n; i++) {
    sum = 0.0;
    for (j = 0; j < n; j++)
        if (i != j)
            sum = sum + abs(a[i][j]);
    if (abs(a[i][i]) < sum) {
        violation_rows[violation_counter]= i;
        violation_counter = violation_counter + 1;
    }
    if (a[i][i] == 0.0) {
        cout << "Found diagonal element equal to zero; rearrange equations; exiting." << endl;
        exit (-1);
    }
}
if (violation_counter > 0) {
    printf ("The Gauss-Seidel convergence criterion is violated in %d rows out of %d\n", violation_counter, n);
    printf ("Specifically, it was violated in rows:\n");
    for (i = 0; i < violation_counter; i++) {
        printf("%d ",violation_rows[i]);
        printf("\n");
    }
    printf("Enter 1 if you want to continue; any other number to abort: ");
    cin >> answer;
    if (answer != 1)
        exit(-1);
    printf ("Check results carefully\n\n");
}
/* initialize the solution vector -- initial guesses */

for (i = 0; i < n; i++) {
    printf ("Enter an initial guess x[%d] of the solution vector: ", i);
    cin >> x[i];
}

/* solve the system */
gauss_seidel (a, b, x, n);

/* output solution */
for (i = 0; i < n; i++) {
    printf ("x[%d]=%f\n", i, x[i]);
}
printf("\n");
return 0;

我在代码中突出了我认为我们关注的部分。以下是有人输入带有trig函数作为输入的内容时输出的示例输出：

 Enter the dimension of the system to be solved: 5

 Enter a[0][0] of the system matrix: 2    
 Enter a[0][1] of the system matrix: sin(3.14/4) 
 Enter a[0][2] of the system matrix:
 Enter a[0][3] of the system matrix:
 Enter a[0][4] of the system matrix:

 Enter b[0] of the right-hand-side vector:
 Enter a[1][0] of the system matrix:
 Enter a[1][1] of the system matrix:
 Enter a[1][2] of the system matrix:
 Enter a[1][3] of the system matrix:
 Enter a[1][4] of the system matrix:

 Enter b[1] of the right-hand-side vector:
 Enter a[2][0] of the system matrix:
 Enter a[2][1] of the system matrix:
 Enter a[2][2] of the system matrix:
 Enter a[2][3] of the system matrix:
 Enter a[2][4] of the system matrix:

 Enter b[2] of the right-hand-side vector:
 Enter a[3][0] of the system matrix:
 Enter a[3][1] of the system matrix:
 Enter a[3][2] of the system matrix:
 Enter a[3][3] of the system matrix:
 Enter a[3][4] of the system matrix:

 Enter b[3] of the right-hand-side vector:
 Enter a[4][0] of the system matrix:
 Enter a[4][1] of the system matrix:
 Enter a[4][2] of the system matrix:
 Enter a[4][3] of the system matrix:
 Enter a[4][4] of the system matrix:

 Enter b[4] of the right-hand-side vector:

 Found diagonal element equal to zero; rearrange equations; exiting. Program ended with exit code:
 255

正如您所看到的，在用户输入[0] [1]的sin函数后，程序完全翻转。这可能是一个很容易解决的新手错误（我在一个介绍课程中如此怜悯），但是我很难理解为什么这些代码确实会出现问题。它的工作方式，以及它为什么不要求用户提供进一步的输入，而是将网格的其余部分初始化为零（我知道其余的代码初始化为零，因为我的收敛标准函数触发器，最后退出程序）。

有人可以向我解释一下吗？

更重要的是，有什么方法可以改变我的代码以允许用户输入像sin（45）或sin（pi / 4）这样的值？

Answer 1

你可以把它作为一个字符串读入每个值，然后你可以用它做任何解析/评估。现在，你要求读一个双，但不要输入一个。

用户输入数组

1 个答案: