# 习题2 # 2.1 x=c(1,2,3) y=c(4,5,6) e=c(rep(1,3)) z=2*x+y+e;z x%*%y # 若x,y如答案那样定义为矩阵,则不能用%*%,因为,维数不对应, x%o%y # 答案 x<-matrix(1:3,nrow=3) y<-matrix(4:6,nrow=3) e<-matrix(c(1,1,1),nrow=3) z<-2*x+y+e;z crossprod(x,y)#内积 outer(x,y)#外积 # 2.2 A=matrix(1:20,4,5);A B=matrix(1:20,4,5,byrow=T);B C=A+B;C D=crossprod(A,B);D# D=A%*%B;D 错误 维数不对应,题目有错,本来就不可能AB E=A*B;E F=A[1:3,1:3];F G=B[,c(1,2,4,5)];G # G<-B[1:4,-3];G 注意-3的用法 # 答案 A<-matrix(1:20,nrow=4) B<-matrix(1:20,nrow=4,byrow=T) C<-A+B;C #D<-AB#不存在AB这种写法 E<-A*B;E F<-A[1:3,1:3];F G<-B[1:4,-3];G # 2.3 x=c(rep(1,5),rep(2,3),rep(3,4),rep(4,2));x #答案同上 # 2.4 Hilbert=function(n=5){ H=matrix(0,nrow=n,ncol=n) for (i in 1:n){ for (j in 1:n) H[i,j]=1/(i+j-1) } H # 返回值, list(Hmatrix=H,det=det(H),sol=solve(H),eig=eigen(H)) # 多元返回值 } H=Hilbert(5);H det(H) solve(H) eigen(H) # 学会了function,对上述进行以下修改 funcH=function(n=5) { H=matrix(0,n,n) for (i in 1:n) { for (j in 1:n) { H[i,j]=1/(i+j-1) } } H # 返回值,输入H # list(Hmatrix=H,det=det(H),sol=solve(H),eig=eigen(H)) # 也可以以列表形式输出多个返回值,同时能给每个元素定义元素名 # 如 list(Hilbert=H) list(Hilbert=H) } funcH() #2.4答案 5价Hilbert矩阵 n<-5 x<-array(0,dim=c(n,n)) for(i in 1:n){ for(j in 1:n){ x[i,j]<-1/(i+j-1) } } x det(x)#矩阵行列式 solve(x)#逆矩阵 eigen(x)#特征值与特征向量 # 2.5 data.frame() studentdata=data.frame(‘姓名‘=c(‘张三‘,‘李四‘,‘王五‘,‘赵六‘,‘丁一‘), ‘性别‘=c(‘女‘,‘男‘,‘女‘,‘男‘,‘女‘),‘年龄‘=c(14,15,16,14,15), ‘身高‘=c(156,165,157,162,159),‘体重‘=c(42,49,41.5,52,45.5)) #studentdata=data.frame(‘序号‘=1:5,‘姓名‘=c(‘张三‘,‘李四‘,‘王五‘,‘赵六‘,‘丁一‘), # ‘性别‘=c(‘女‘,‘男‘,‘女‘,‘男‘,‘女‘),‘年龄‘=c(14,15,16,14,15), # ‘身高‘=c(156,165,157,162,159),‘体重‘=c(42,49,41.5,52,45.5)) # 不需要输入序号。 write.table(studentdata,‘Re2.5.txt‘) # 答案 student<-data.frame(name=c("zhangsan","lisi","wangwu","zhaoliu","dingyi"), sex=c("f","m","f","m","f"), age=c("14","15","16","14","15"), height=c("156","165","157","162","159"), weight=c("42","49","41.5","52","45.5")) # 2.6 st=read.table(‘Re2.5.txt‘,header=T) write.csv(st,‘Re2.5.csv‘) #2.6 答案 student1<-write.table(student,file="student1.txt") student2<-read.table("student1.txt",head=T) student3<-write.csv(student2,file="student3.csv") # 2.7 func=function(n) { if (n<=0) "要求输入一个正整数" else { while(n!=1) { if (n%%2==0) n=n/2 else n=3*n+1} "运算成功" } } # R中定义的函数,没有专门的返回值设置,只相当于代码复制粘贴, func(8) #返回值为代码的输出值 # 答案 #2.7 func<-function(n){ if(n<=0) list("要求输入一个正整数") else{ repeat{ if(n==1) break else if(n%%2==0){n<-n/2} else n<-3*n+1} list("运算成功") } }
时间: 2024-10-04 00:43:40