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如何打印 JAMA 矩阵的列？

发布于 2024-07-14 16:06:51 字数 34 浏览 7 评论 0原文

我使用 JAMA.matrix 包..如何打印矩阵的列

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在风中等你 2024-07-21 16:06:52

最简单的方法可能是转置矩阵，然后打印每一行。取 API 中的示例的一部分：

double[][] vals = {{1.,2.,3},{4.,5.,6.},{7.,8.,10.}};
Matrix a = new Matrix(vals);
Matrix aTransposed = a.transpose();
double[][] valsTransposed = aTransposed.getArray();

// now loop through the rows of valsTransposed to print
for(int i = 0; i < valsTransposed.length; i++) {
    for(int j = 0; j < valsTransposed[i].length; j++) {        
        System.out.print( " " + valsTransposed[i][j] );
    }
}

正如 duffymo 指出的在注释中，绕过转置并仅编写嵌套的 for 循环来打印列而不是跨行会更有效。如果您需要两种方式打印，则会导致代码量增加一倍。这是一个足够常见的权衡（速度与代码大小），我将其留给您来决定。

The easiest way would probably be to transpose the matrix, then print each row. Taking part of the example from the API:

double[][] vals = {{1.,2.,3},{4.,5.,6.},{7.,8.,10.}};
Matrix a = new Matrix(vals);
Matrix aTransposed = a.transpose();
double[][] valsTransposed = aTransposed.getArray();

// now loop through the rows of valsTransposed to print
for(int i = 0; i < valsTransposed.length; i++) {
    for(int j = 0; j < valsTransposed[i].length; j++) {        
        System.out.print( " " + valsTransposed[i][j] );
    }
}

As duffymo pointed out in a comment, it would be more efficient to bypass the transposition and just write the nested for loops to print down the columns instead of across the rows. If you need to print both ways that would result in twice as much code. That's a common enough tradeoff (speed for code size) that I leave it to you to decide.

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醉态萌生 2024-07-21 16:06:52

您可以在矩阵上调用 getArray() 方法来获取表示元素的 double[][]。
然后您可以循环该数组以显示您想要的任何列/行/元素。

有关更多方法，请参阅 API。

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装纯掩盖桑 2024-07-21 16:06:52

public static String strung(Matrix m) {
    StringBuffer sb = new StringBuffer();
    for (int r = 0; r < m.getRowDimension(); ++ r) {
        for (int c = 0; c < m.getColumnDimension(); ++c)
            sb.append(m.get(r, c)).append("\t");
        sb.append("\n");
    }
    return sb.toString();
}

public static String strung(Matrix m) {
    StringBuffer sb = new StringBuffer();
    for (int r = 0; r < m.getRowDimension(); ++ r) {
        for (int c = 0; c < m.getColumnDimension(); ++c)
            sb.append(m.get(r, c)).append("\t");
        sb.append("\n");
    }
    return sb.toString();
}

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