在Matlab矩阵中设置元素的精度 [英] Set precision an element in Matlab matrix

问题描述

我想为矩阵的所有元素设置精度.以下是我的工作:

I want to set precision for all element of a matrix. Below is what I did:

>>A

A =

         0    1.0000         0         0         0         0
 -137.0830         0         0         0         0         0
         0         0         0    1.0000         0         0
  365.5546         0         0         0         0         0
         0         0         0         0         0    1.0000
  365.5546         0         0         0         0         0

>> vpa(A,2)

ans =

[      0, 1.0, 0,   0, 0,   0]
[ -144.0,   0, 0,   0, 0,   0]
[      0,   0, 0, 1.0, 0,   0]
[  377.0,   0, 0,   0, 0,   0]
[      0,   0, 0,   0, 0, 1.0]
[  377.0,   0, 0,   0, 0,   0]

结果不是我的愿望，应该是: -第一列中的-137.08、365.55、365.55. 请帮助建议我如何获得它. 非常感谢！

The result is not my desire, it should be: -137.08, 365.55, 365.55 in the first column. Please help to suggest me how to get it. Thank you so much!

推荐答案

您没有正确使用vpa.从文档:

vpa(x，d)使用至少d个有效数字

vpa(x,d) uses at least d significant digits

注意至少说 .这就是为什么当您只要求输入2个有效数字时仍然得到377的原因.

Nota that it says at least. That is why you still get 377 when you only asked for 2 significant digits.

您似乎不知道有效数字是多少.来自维基百科:

It seems that you don't know what significant digits are. From Wikipedia:

数字的有效数字是带有含义的数字 有助于其测量分辨率.这包括所有数字 除了:

The significant figures of a number are digits that carry meaning contributing to its measurement resolution. This includes all digits except:

• 所有前导零；
• 在零仅用作占位符时指示数字的刻度(精确规则在识别时说明) 重要数字)；和
• 例如通过比原始数据或测量更高的精度进行计算而引入的虚假数字 报告的精度要比设备支持的精度高.

• All leading zeros;
• Trailing zeros when they are merely placeholders to indicate the scale of the number (exact rules are explained at identifying significant figures); and
• Spurious digits introduced, for example, by calculations carried out to greater precision than that of the original data, or measurements reported to a greater precision than the equipment supports.

所以你想要这个

>> vpa(365.5546, 5)
ans =
365.55

现在，要保持一致，您需要找出矩阵的最大值，然后

Now, to be consistent, you need to find out what is the maximum of your matrix and compute the desired number of significant digits from there.

max_number = floor(log10(max(abs(A(:))+1)) + 1);
decimals = 2;
vpa(A, max_number + decimals)

在这里，max_number是矩阵具有的整数位的最大位数，而decimals是要具有的小数位数.

Here, max_number is the maximum number of integer digits that your matrix has, and decimals is the number of decimal places that you want to have.

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