update_a_ic: Update one element of scores A
In krisrs1128/expPCA: Exponential Family PCA

Update one element of scores A

1	update_a_ic(obj_fun, obj_grad_a, x_i, a_ic, v_c, s_i, lambda, mu0)

`obj_fun`	Version of loss given by bregman divergence between data and link to use in current updates.
`obj_grad_a`	Gradient of the provided loss, with respect to a.
`x_i`	The i^th sample of X.
`a_ic`	The initial value of a_ic to start the search from.
`v_c`	The c^th component of V.
`s_i`	The s^th row of the matrix AV^T - a_cv_c^T
`lambda`	The regularization parameter in the optimizatyion.
`mu0`	The value to regularize towards.