> x=c(7.3, 6.8, 0.005, 9, 12, 2.4, 18.9, 0.9)
> mean(x)
[1] 7.163125
> y=x-mean(x)
> y
[1] 0.136875 -0.363125 -7.158125 1.836875 4.836875 -4.763125
[7] 11.736875 -6.263125
w=x[x>sqrt(x)]
> w
[1] 7.3 6.8 9.0 12.0 2.4 18.9
> round(sqrt(x),2)
[1] 2.70 2.61 0.07 3.00 3.46 1.55 4.35 0.95
>
2.计算 2 的前 50 次方和 1到50的平方。这两个序列有那几个元素相等?
> z=1:50
> a=2^(1/z)
> b=2^z
> c=a-b
> > z[c==0]
[1] 1
3.请将一个数值型向量在2的倍数的位置上的元素变为这个元素的负值。
> q=1:100
> s=ifelse(q%%2==0,-q,q)
> s
[1] 1 -2 3 -4 5 -6 7 -8 9 -10 11
[12] -12 13 -14 15 -16 17 -18 19 -20 21 -22
[23] 23 -24 25 -26 27 -28 29 -30 31 -32 33
[34] -34 35 -36 37 -38 39 -40 41 -42 43 -44
[45] 45 -46 47 -48 49 -50 51 -52 53 -54 55
[56] -56 57 -58 59 -60 61 -62 63 -64 65 -66
[67] 67 -68 69 -70 71 -72 73 -74 75 -76 77
[78] -78 79 -80 81 -82 83 -84 85 -86 87 -88
[89] 89 -90 91 -92 93 -94 95 -96 97 -98 99
[100] -100
4.写出一个函数计算数值型向量的方差,数值向量为(12,3,5,3,2,5,3,6,3,6,2,7,4)
> f=c(12,3,5,3,2,5,3,6,3,6,2,7,4)
> v=(sum((f-mean(f))^2))/(length(f)-1)
> v
[1] 7.397436
> var(f)
[1] 7.397436
5.存在下面的矩阵,使用R语言求出矩阵的逆阵,特征根,特征向量
1.00 0.80 0.26 0.67 0.34 0.80 1.00 0.33 0.59 0.34 0.26 0.33 1.00 0.37 0.21 0.67 0.59 0.37 1.00 0.35 0.34 0.34 0.21 0.35 1.00
> h=c(1.00 , 0.80 , 0.26 , 0.67 , 0.34 ,0.80 , 1.00 , 0.33 , 0.59 , 0.34 ,0.26 , 0.33 , 1.00 , 0.37 , 0.21 ,0.67 , 0.59 ,0.37, 1.00 , 0.35, 0.34, 0.34, 0.21, 0.35, 1.00 )
> hh=matrix(h,nrow=5,ncol=5,byrow=T)
> solve(hh)
[,1] [,2] [,3] [,4] [,5]
[1,] 3.3881372 -2.1222233 0.23706087 -1.0684729 -0.10622799
[2,] -2.1222233 2.9421167 -0.33593309 -0.1330915 -0.16163579
[3,] 0.2370609 -0.3359331 1.20698521 -0.3763728 -0.08811984
[4,] -1.0684729 -0.1330915 -0.37637284 2.0091273 -0.21562437
[5,] -0.1062280 -0.1616358 -0.08811984 -0.2156244 1.18504738
> eigen(hh)
$values
[1] 2.7922569 0.8263366 0.7790638 0.4205873 0.1817554
$vectors
[,1] [,2] [,3] [,4] [,5]
[1,] -0.5255426 0.3402197 -0.1665086 0.15937771 0.74493565
[2,] -0.5186716 0.2343491 -0.1777739 0.50822995 -0.62141694
[3,] -0.3131429 -0.9030775 -0.2287038 0.14942789 0.10843643
[4,] -0.4966433 0.0386900 -0.1185744 -0.83115510 -0.21672526
[5,] -0.3317705 -0.1108387 0.9350433 0.05615655 0.01354831
>