returns log-density of convolution of each component of a normal mixture with N(0,s^2) or s*t(v) at x. Note that convolution of two normals is normal, so it works that way
# S3 method for normalmix
log_comp_dens_conv(m, data)
a k by n matrix
mixture distribution with k components
a list with components x and s to be interpreted as a normally-distributed observation and its standard error