help to fix this numeric symbolic array
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I need some help with the code below:
scaleFactors = [ 3.4, 2.3;
1.7, 1.9 ]
xMatSym = sym('X',[ 2, 2 ]);
xScaled = xMatSym./scaleFactors;
I am hoping to get the results shown below:
X1_1/3.4 X1_2/2.3
X2_1/1.7 X2_2/1.9
But, instead I am getting the results below instead:
(5*X1_1)/17 (10*X1_2)/23
(10*X2_1)/17 (10*X2_2)/19
I know the reasons it doesn't work. But I don't know how to fix this. Can someone help me?
Thank you so much!
3 个评论
I've used the "{} code" button to format the code and the numbers. Do you see that this improves the readability? Please use this by your own in the future.
What does "fixing" mean, if the current results are correct? 5*x/17 is the same as x/3.4 mathematically. Working with integer numbers is more accurate from the view point of numerics.
I've looked at doc sym: conversion techniques, but have too few experiences with the symbolic toolbox to adjust the display as wanted.
Lisa Lee
2017-8-12
回答（1 个）
Karan Gill
2017-8-12
编辑：Karan Gill
2017-10-17
0 个投票
You can't have a "numeric symbolic" array because "numeric" and "symbolic" are different data types. For your options, see https://www.mathworks.com/help/symbolic/choose-symbolic-or-numeric-arithmetic.html.
Instead, try the vpa function on your result.
2 个评论
Walter Roberson
2017-8-12
Note that vpa(xScaled) will get you output such as
[ 0.29411764705882352941176470588235*X1_1, 0.43478260869565217391304347826087*X1_2]
[ 0.58823529411764705882352941176471*X2_1, 0.52631578947368421052631578947368*X2_2]
You can also
>> vpa(xScaled,2)
ans =
[ 0.29*X1_1, 0.43*X1_2]
[ 0.59*X2_1, 0.53*X2_2]
Notice these are multiplications, not divisions, and it does matter for precision purposes how many digits you truncate to.
>> 1000/1.7
ans =
588.235294117647
>> 1000*.59
ans =
590
Karan Gill
2017-8-13
Yes, I do not recommend using vpa(xScaled,2) to anyone who hasn't carefully read the vpa doc :) Too much potential for confusion.
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