Matt, I know you are probably busy with work, but I cannot help buy asking you these R questions. If it is bothersome, please let me know and I will stick with the R help... but I have two matrices X [,1] [,2] [,3] [,4] [,5] [,6] [1,] 660 693.00 726.0 759.00 792.0 825.00 [2,] 548 575.40 602.8 630.20 657.6 685.00 [3,] 676 709.80 743.6 777.40 811.2 845.00 [4,] 763 801.15 839.3 877.45 915.6 953.75 [5,] 768 806.40 844.8 883.20 921.6 960.00 [6,] 692 726.60 761.2 795.80 830.4 865.00 [7,] 657 689.85 722.7 755.55 788.4 821.25 [8,] 630 661.50 693.0 724.50 756.0 787.50 [9,] 748 785.40 822.8 860.20 897.6 935.00 [10,] 680 714.00 748.0 782.00 816.0 850.00 and Y [,1] [,2] [,3] [,4] [,5] [,6] [1,] 1369.00 1396.517 1424.308 1452.372 1480.710 1509.323 [2,] 1521.00 1551.572 1582.448 1613.629 1645.114 1676.903 [3,] 1521.00 1551.572 1582.448 1613.629 1645.114 1676.903 [4,] 1521.00 1551.572 1582.448 1613.629 1645.114 1676.903 [5,] 1600.00 1632.160 1664.640 1697.440 1730.560 1764.000 [6,] 1722.25 1756.867 1791.829 1827.135 1862.786 1898.781 [7,] 1936.00 1974.914 2014.214 2053.902 2093.978 2134.440 [8,] 2025.00 2065.703 2106.810 2148.323 2190.240 2232.563 [9,] 2116.00 2158.532 2201.486 2244.864 2288.666 2332.890 [10,] 2209.00 2253.401 2298.244 2343.528 2389.254 2435.423 Each row (1-10) is an individual and columns 1-6 are treatments to each individual. I need to look at interactions between the two variables X and Y, by rows example 1369 + (660*1369 ^ -1) 1396.517 + (660*1396.517 ^ -1) 1424.308 + (660*1424.308 ^ -1) ... 1369 + (693*1369 ^ -1 1396.517 + (693*1396.517 ^ -1 1424.308 + (693*1424.308 ^ -1 ... etc. so each row would yield 36 numbers. I have the following which works for X/Y, but I need Y+X/Y num.x.col <- length(X[1,]) num.y.col <- length(Y[1,]) num.rows <- length(X[,1]) Z <- matrix(nrow=num.rows, ncol=num.x.col*num.y.col) for( i in 1:num.rows) { Z[i,] <- as.vector(X[i,] %*% t(Y[i,])^-1 ) } Any help with making this be Y + X/Y would be appreciated. -- Keith Cox, Ph.D. Sitka Sound Science Center Fisheries Biologist P.O. Box 464 Sitka, Alaska, 99835 907 752-0563 marlinkcox@gmail.com [[alternative HTML version deleted]]