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<div>Hello, when I look at IJacobian function in the example: <a href="http://www.mcs.anl.gov/petsc/petsc-current/src/ts/examples/tutorials/ex19.c"><font color="#0000FF"><u>http://www.mcs.anl.gov/petsc/petsc-current/src/ts/examples/tutorials/ex19.c</u></font></a></div>
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<div><font face="Courier New, monospace" size="2">static PetscErrorCode IJacobian(TS ts,PetscReal t,Vec X,Vec Xdot,PetscReal a,Mat *A,Mat *B,MatStructure *flag,void *ctx)</font></div>
<div><font face="Courier New, monospace" size="2">{</font></div>
<div><font face="Courier New, monospace" size="2"> PetscErrorCode ierr;</font></div>
<div><font face="Courier New, monospace" size="2"> PetscInt rowcol[] = {0,1};</font></div>
<div><font face="Courier New, monospace" size="2"> PetscScalar *x,J[2][2];</font></div>
<div><font face="Courier New, monospace" size="2"> </font></div>
<div><font face="Courier New, monospace" size="2"> PetscFunctionBeginUser;</font></div>
<div><font face="Courier New, monospace" size="2"> ierr = VecGetArray(X,&x);CHKERRQ(ierr);</font></div>
<div><font face="Courier New, monospace" size="2"> J[0][0] = a; J[0][1] = -1.;</font></div>
<div><font face="Courier New, monospace" size="2"> J[1][0] = 1.; J[1][1] = -1. + x[1]*x[1];</font></div>
<div><font face="Courier New, monospace" size="2"> ierr = MatSetValues(*B,2,rowcol,2,rowcol,&J[0][0],INSERT_VALUES);CHKERRQ(ierr);</font></div>
<div><font face="Courier New, monospace" size="2"> ierr = VecRestoreArray(X,&x);CHKERRQ(ierr);</font></div>
<div><font face="Courier New, monospace" size="2"> </font></div>
<div><font face="Courier New, monospace" size="2"> ierr = MatAssemblyBegin(*A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);</font></div>
<div><font face="Courier New, monospace" size="2"> ierr = MatAssemblyEnd(*A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);</font></div>
<div><font face="Courier New, monospace" size="2"> if (*A != *B) {</font></div>
<div><font face="Courier New, monospace" size="2"> ierr = MatAssemblyBegin(*B,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);</font></div>
<div><font face="Courier New, monospace" size="2"> ierr = MatAssemblyEnd(*B,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);</font></div>
<div><font face="Courier New, monospace" size="2"> }</font></div>
<div><font face="Courier New, monospace" size="2"> *flag = SAME_NONZERO_PATTERN;</font></div>
<div><font face="Courier New, monospace" size="2"> PetscFunctionReturn(0);</font></div>
<div><font face="Courier New, monospace" size="2">}</font></div>
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<div>There’s a PetscReal a. Is it a constant? And if the value of a known outside of the IJacobian function, saying the main() part.</div>
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<div>If it is, then as shown in this example, <font face="Courier New, monospace" size="2">J[0][0] = a;</font><font face="Courier New, monospace" size="2"> </font><font face="Courier New, monospace" size="2">J[0][1] = -1.; J[1][0] = 1.;</font><font face="Courier New, monospace" size="2">
are constant through all the iterations. How can I use Mat</font><font face="Courier New, monospace" size="2">RetrieveValues(*A) and MatStoreValue</font><font face="Courier New, monospace" size="2">s(*A) to reuse them?</font></div>
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<div><font face="Courier New, monospace" size="2">I’m asking this question because I have a large Jacobian matrix, but half of the matrix contains constant values. However, I don’t know what’s “PetscReal a” when I try to use it to compute my constant elements
of Jacobian matrix which doesn’t depend on the value of x at all.</font></div>
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<div><font face="Courier New, monospace" size="2">Thanks,</font></div>
<div><font face="Courier New, monospace" size="2">Shuangshuang</font></div>
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