**petsc-main 2021-04-20**

# SNESLINESEARCHNCGLINEAR

Special line search only for SNESNCG This line search uses the length "as if" the problem is linear (that is what is computed by the linear CG method) using the Jacobian of the function.
alpha = (r, r) / (p, Ap) = (f, f) / (y, Jy) where r (f) is the current residual (function value), p (y) is the current search direction.
Notes: This requires a Jacobian-vector product but does not require the solution of a linear system with the Jacobian

This is a "odd-ball" line search, we don't know if it is in the literature or used in practice by anyone.

### See Also

SNESLineSearchCreate(), SNESLineSearchSetType()

### Level

advanced

### Location

src/snes/impls/ncg/snesncg.c

Index of all SNES routines

Table of Contents for all manual pages

Index of all manual pages