PETSc version 3.17.4
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# TSSetIFunction

Set the function to compute F(t,U,U_t) where F() = 0 is the DAE to be solved.

### Synopsis

    #include "petscts.h"
    PetscErrorCode  TSSetIFunction(TS ts,Vec r,TSIFunction f,void *ctx)

Logically Collective on TS

### Input Parameters

| ts | - the TS context obtained from TSCreate()
| r | - vector to hold the residual (or NULL to have it created internally)
| f | - the function evaluation routine
| ctx | - user-defined context for private data for the function evaluation routine (may be NULL)

### Calling sequence of f

        PetscErrorCode f(TS ts,PetscReal t,Vec u,Vec u_t,Vec F,ctx);

| t | - time at step/stage being solved
| u | - state vector
| u_t | - time derivative of state vector
| F | - function vector
| ctx | - [optional] user-defined context for matrix evaluation routine

### Important

The user MUST call either this routine or TSSetRHSFunction() to define the ODE. When solving DAEs you must use this function.

### See Also

TSSetRHSJacobian(), TSSetRHSFunction(), TSSetIJacobian()

### Level

beginner

### Location

src/ts/interface/ts.c

### Examples

src/ts/tutorials/ex3.c.html
src/ts/tutorials/ex8.c.html
src/ts/tutorials/ex10.c.html
src/ts/tutorials/ex14.c.html
src/ts/tutorials/ex15.c.html
src/ts/tutorials/ex16.c.html
src/ts/tutorials/ex17.c.html
src/ts/tutorials/ex19.c.html
src/ts/tutorials/ex20.c.html
src/ts/tutorials/ex22.c.html
src/ts/tutorials/ex23fwdadj.c.html
Index of all TS routines
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Index of all manual pages