> x <- matrix(rnorm(16), 4, 4)
> x
           [,1]        [,2]       [,3]       [,4]
[1,] -0.0842049 -1.06362689  0.6288775  0.2320943
[2,] -1.3221870  1.16087586  1.2201729  0.3863462
[3,] -0.8579952  0.60189344 -0.9718385  0.5811132
[4,] -0.1639939  0.01828404 -0.8832882 -0.4239814
> y <- format(x, digits = 2)
> write.csv(y, file = "a.csv")

非常感谢版主