Hello, I tried to do a 'sem' analysis for data of how blueberry consumption
by birds is influenced by a pollution gradient, using distance and
vegetation structural and composition variables, but I got the following
error message:
Error in sem.default(ram = ram, S = S, N = N, param.names = pars, var.names
= vars, :
S must be a square triangular or symmetric matrix
This may be very obvious for R specialist, but I cant find the problem!
#Symbolic ram model
mod.BB.1 <- specify.model()
BB.Cob -> B.B, lamb1, NA
Under.Cob -> B.B, lamb2, NA
BA -> B.B, lamb3, NA
Over.Comp -> B.B, lamb4, NA
Under.Comp -> B.B, lamb5, NA
Site -> B.B, lamb6, NA
Site -> BB.Cob, lamb7, NA
Site -> BA, lamb8, NA
Site -> Under.Cob, lamb9, NA
Site -> Under.Comp, lamb10, NA
Site -> Under.Comp, lamb11, NA
Under.Comp <-> Over.Comp, beta1, NA
Under.Cob <-> BA, beta2, NA
BB.Cob <-> BB.Cob, beta3, NA
Under.Cob <-> Under.Cob, beta4, NA
BA <-> BA, beta5, NA
Under.Comp <-> Under.Comp, beta6, NA
Over.Comp <-> Over.Comp, beta7, NA
B.B <-> B.B, beta8, NA
Site <-> Site, NA, 1
#S matrix
S.Seed.BB <- matrix(c(
2.243, 3.055, 1.657, -2.166, 12.424, 27.105, 2.205,
3.055, 41.942, 2.079, -2.392, 15.390, 37.759, 0.565,
1.657, 2.079, 1.396, -1.655, 9.960, 15.360, -1.238,
-2.166, -2.392, -1.655, 2.164, -12.328, -25.099, -1.791,
12.424, 15.390, 9.960, -12.328, 72.492, 129.491, -0.004,
27.105, 37.758, 15.360, -25.099, 129.491, 456.913, 108.861,
2.205, 0.565, -1.238, -1.791, -0.004, 108.861, 56.239),7,7,byrow=TRUE)
rownames(S.Seed.BB) <- colnames(S.Seed.BB) <-
c('Site','B.B','Over.Comp','Under.Comp','BA','Under.Cob', 'BB.Cob')
#sem function
sem.BB.1 <- sem(mod.BB.1, S.Seed.BB, N=40)
Thanks a lot for any suggestions!
-----
Biol. Verónica Chillo
Grupo de Investigaciones de la Biodiversidad (GIB)
Instituto Argentino de Investigaciones de Zonas Áridas (IADIZA) - CCT Mendoza,
CONICET, Argentina
Av. Ruíz Leal s/n, Parque San Martín, (CP5500) Mendoza Ciudad, Mendoza,
Argentina.
Tel. +54-261-5244130
http://personal.cricyt.edu.ar/vchillo/
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