CODEWITHSUNDEEP
rmatrix
DevStudent55
DevStudent55

Reputation: 13

Incorrect result when multiping matrixes in R?

I'm getting some weird results when multiplying these two matrices in R:

> matrix3

    [1,]  3.19747172 -2.806e-05 -0.00579284 -0.00948720 -0.01054026  0.17575719
    [2,] -0.00002806  2.000e-08  0.00000057  0.00000006 -0.00000009 -0.00000358
    [3,] -0.00579284  5.700e-07  0.00054269  0.00001793 -0.00002686 -0.00310465
    [4,] -0.00948720  6.000e-08  0.00001793  0.00003089  0.00002527 -0.00066290
    [5,] -0.01054026 -9.000e-08 -0.00002686  0.00002527  0.00023776 -0.00100898
    [6,]  0.17575719 -3.580e-06 -0.00310465 -0.00066290 -0.00100898  0.03725362

> matrix4
              [,1]
    x0    2428.711
    x1 1115178.561
    x2   74411.013
    x3  925700.445
    x4   74727.396
    x5   13342.182

> matrix3%*%matrix4
                  [,1]
    [1,] 78.4244581753
    [2,] -0.0023802299
    [3,]  0.1164568885
    [4,] -0.0018504732
    [5,] -0.0006493249
    [6,] -0.1497822396

The thing is that if you try to multiply these two matrices in excel you get:

>78.4824494081686
>-0.0000419022486847151
>0.112430295996347
>-0.000379343461780479
>0.000340414687578061
>-0.14454024116344

And using online matrices I also got to excel's result. Would love your help in understanding how to get the same result in R.

Upvotes: 0

Views: 226

Answers (1)

DevStudent55
DevStudent55

Reputation: 13

The problem occurred due to the use of the function inv() from the library(matlib). matrix3 is a result of inversing using the inv() function. Not sure why when I used solve() to inverse and then continued normally I got the correct matrix. Perheps there is some kind of rounding in the inv() function.

Upvotes: 1

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