Simulacion_Esfera

#########################################################################################
library("plot3D");
#########################################################################################
grid_size = 60;
eps = 0.01;
theta = seq(0+eps,pi-eps,l=grid_size);
phi = seq(0,2*pi-eps,l=grid_size);
coord = expand.grid(phi,theta);
x = sin(coord[,2])*cos(coord[,1]);
y = sin(coord[,2])*sin(coord[,1]);
z = cos(coord[,2]);
nsites = length(x);


cova <- function(escala,geod){

  res = exp(-3*geod/escala);
  return(res)
}

val = 0.99999999999;
escala = 1;
mat = array(dim=c(nsites,nsites));

for(i in 1:nsites){
  for(j in 1:nsites){

    prod = x[i]*x[j]+y[i]*y[j]+z[i]*z[j];
    if(prod > val){dij = 0;}
    if(prod < -val){dij = pi;}
    if(prod <= val & prod >= -val){dij = acos(prod);}

    mat[i,j] = cova(escala,dij);

  }
}

set.seed(8756)
datos = t(chol(mat))%*%rnorm(nsites);

scatter3D(x,y,z,colvar=datos)