A.12 Basic Math Functions

abs        # absolute value
round      # 반올림반버림, round to even number (IMPORTANT !!!)
floor      # 버림
ceiling    # 올림
exp        # exponential
log        # logarithmic
sqrt       # square root
min        # minimum
max        # maximum
mean       # average
median     # median
sum        # summation
cumsum     # cumulative summation
colSums    # sums by columns
colMeans   # means by columns
rowSums    # sums by rows
rowMeans   # means by rows
choose     # combination
scale      # normalize, standardize
crossprod  # cross product of matrix, X'X or X'Y
det        # determiant of a matrix
diag       # diagonal vector of a matrix or construct a diagonal matrix
eigen      # eigenvalues and eigenvectors by spectral decomposition
solve      # inverse of a matrix
qr         # QR decomposition
svd        # singular value decomposition

수학적 표현들을 어떻게 R로 표현하는가 하는 것은 제 1장을 참고한다.