simpost_IS: Mass marginal posterior density with the Laplace...
In sgolchi/BPD: Bayesian Particle Discovery

Mass marginal posterior density with the Laplace approximation with importance weights under "no Higgs" assumption

1	simpost_IS(j, p0, G, snew, cnew, covmat, lambda_mean)

`j`	index
`p0`	prior mass on `m = 0`
`G`	grid over which the signal is evaluated
`snew`	matrix of signal widths, same dimensions as `cnew`
`cnew`	matrix of signal normalizing constants - dimensions are (size of grid `G`)by(number of categories/channels,41)
`covmat`	covariance matrix for teh background prior
`lambda_mean`	mean vector for the background prior
`lambda0`	initial backgorund value
`y`	observations