# sqrtm: Matrix Square and p-th Roots

### Description

Computes the matrix square root and matrix p-th root of a nonsingular real matrix.

D <- diag(E\$values) B <- V %*% D^(1/p) %*% U or by applying the functions expm, logm in package ‘expm’: B <- expm(1/p * logm(A)) As these approaches all calculate the principal branch, the results are identical (but will numerically slightly differ). ### References N. J. Higham (1997). Stable Iterations for the Matrix Square Root. Numerical Algorithms, Vol. 15, pp. 227–242. D. A. Bini, N. J. Higham, and B. Meini (2005). Algorithms for the matrix pth root. Numerical Algorithms, Vol. 39, pp. 349–378. ### See Also expm, expm::sqrtm ### Examples   1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 A1 <- matrix(c(10, 7, 8, 7, 7, 5, 6, 5, 8, 6, 10, 9, 7, 5, 9, 10), nrow = 4, ncol = 4, byrow = TRUE) X <- sqrtm(A1)$B # accuracy: 2.352583e-13 X A2 <- matrix(c(90.81, 8.33, 0.68, 0.06, 0.08, 0.02, 0.01, 0.01, 0.70, 90.65, 7.79, 0.64, 0.06, 0.13, 0.02, 0.01, 0.09, 2.27, 91.05, 5.52, 0.74, 0.26, 0.01, 0.06, 0.02, 0.33, 5.95, 85.93, 5.30, 1.17, 1.12, 0.18, 0.03, 0.14, 0.67, 7.73, 80.53, 8.84, 1.00, 1.06, 0.01, 0.11, 0.24, 0.43, 6.48, 83.46, 4.07, 5.20, 0.21, 0, 0.22, 1.30, 2.38, 11.24, 64.86, 19.79, 0, 0, 0, 0, 0, 0, 0, 100 ) / 100, nrow = 8, ncol = 8, byrow = TRUE) X <- rootm(A2, 12) # k = 6, accuracy: 2.208596e-14 ## Matrix sign function signm(A1) # 4x4 identity matrix B <- rbind(cbind(zeros(4,4), A1), cbind(eye(4), zeros(4,4))) signm(B) # [0, signm(A1)$B; signm(A1)$Binv 0] 

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