Function SCIPevalExprHessianDir 

pub unsafe extern "C" fn SCIPevalExprHessianDir(
    scip: *mut SCIP,
    expr: *mut SCIP_EXPR,
    sol: *mut SCIP_SOL,
    soltag: c_longlong,
    direction: *mut SCIP_SOL,
) -> SCIP_RETCODE

evaluates Hessian-vector product of an expression for a given point and direction

Evaluates children, if necessary. Value can be received via SCIPgetExprPartialDiffGradientDirNonlinear(). If an error (division by zero, …) occurs, this value will be set to SCIP_INVALID.