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# SNESLINESEARCHNCGLINEAR

Special line search only for the nonlinear CG solver `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

SNES: Nonlinear Solvers, `SNES`, `SNESNCG`, `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