Function SCIPcallExprCurvature 

pub unsafe extern "C" fn SCIPcallExprCurvature(
    scip: *mut SCIP,
    expr: *mut SCIP_EXPR,
    exprcurvature: SCIP_EXPRCURV,
    success: *mut c_uint,
    childcurv: *mut SCIP_EXPRCURV,
) -> SCIP_RETCODE

calls the curvature callback for an expression

@see SCIP_DECL_EXPRCURVATURE

Returns unknown curvature if callback not implemented.