# PetIGA / demo / BoundaryIntegral.c

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139``` ```/* This code solves the Laplace problem where the boundary conditions can be changed from Nuemann to Dirichlet via the commandline. While its primary use is in regression tests for PetIGA, it also demonstrates how boundary integrals may be performed to enforce things like Neumann conditions. keywords: steady, scalar, linear, testing, dimension independent, boundary integrals */ #include "petiga.h" #undef __FUNCT__ #define __FUNCT__ "System" PetscErrorCode System(IGAPoint p,PetscScalar *K,PetscScalar *F,void *ctx) { PetscInt nen,dim; IGAPointGetSizes(p,0,&nen,0); IGAPointGetDims(p,&dim,0,0); const PetscReal *N1; IGAPointGetShapeFuns(p,1,&N1); PetscInt a,b,i; for (a=0; ashape[0]; PetscInt a,nen=p->nen; for (a=0; aside == 0) x = 1 - p->point[user->dir]; else x = p->point[user->dir]; PetscReal e = u - x; S[0] = e*e; return 0; } #undef __FUNCT__ #define __FUNCT__ "main" int main(int argc, char *argv[]) { PetscErrorCode ierr; ierr = PetscInitialize(&argc,&argv,0,0);CHKERRQ(ierr); AppCtx user; user.dir = 0; user.side = 1; ierr = PetscOptionsBegin(PETSC_COMM_WORLD,"","Options","IGA");CHKERRQ(ierr); ierr = PetscOptionsInt("-dir", "direction",__FILE__,user.dir, &user.dir, PETSC_NULL);CHKERRQ(ierr); ierr = PetscOptionsInt("-side","side", __FILE__,user.side,&user.side,PETSC_NULL);CHKERRQ(ierr); ierr = PetscOptionsEnd();CHKERRQ(ierr); IGA iga; ierr = IGACreate(PETSC_COMM_WORLD,&iga);CHKERRQ(ierr); ierr = IGASetDof(iga,1);CHKERRQ(ierr); IGABoundary bnd; PetscInt d = !user.side; PetscInt n = !!user.side; ierr = IGAGetBoundary(iga,user.dir,d,&bnd);CHKERRQ(ierr); ierr = IGABoundarySetValue(bnd,0,0.0);CHKERRQ(ierr); ierr = IGAGetBoundary(iga,user.dir,n,&bnd);CHKERRQ(ierr); ierr = IGABoundarySetUserSystem(bnd,Neumann,PETSC_NULL);CHKERRQ(ierr); ierr = IGASetFromOptions(iga);CHKERRQ(ierr); ierr = IGASetUp(iga);CHKERRQ(ierr); Mat A; Vec x,b; ierr = IGACreateMat(iga,&A);CHKERRQ(ierr); ierr = IGACreateVec(iga,&x);CHKERRQ(ierr); ierr = IGACreateVec(iga,&b);CHKERRQ(ierr); ierr = IGASetUserSystem(iga,System,PETSC_NULL);CHKERRQ(ierr); ierr = IGAComputeSystem(iga,A,b);CHKERRQ(ierr); KSP ksp; ierr = IGACreateKSP(iga,&ksp);CHKERRQ(ierr); ierr = KSPSetOperators(ksp,A,A,SAME_NONZERO_PATTERN);CHKERRQ(ierr); ierr = KSPSetFromOptions(ksp);CHKERRQ(ierr); ierr = KSPSolve(ksp,b,x);CHKERRQ(ierr); PetscInt dim; ierr = IGAGetDim(iga,&dim);CHKERRQ(ierr); if (dim <= 2) {ierr = VecView(x,PETSC_VIEWER_DRAW_WORLD);CHKERRQ(ierr);} PetscScalar error = 0; ierr = IGAFormScalar(iga,x,1,&error,Error,&user);CHKERRQ(ierr); error = PetscSqrtReal(PetscRealPart(error)); ierr = PetscPrintf(PETSC_COMM_WORLD,"L2 error = %G\n",error);CHKERRQ(ierr); ierr = KSPDestroy(&ksp);CHKERRQ(ierr); ierr = MatDestroy(&A);CHKERRQ(ierr); ierr = VecDestroy(&x);CHKERRQ(ierr); ierr = VecDestroy(&b);CHKERRQ(ierr); ierr = IGADestroy(&iga);CHKERRQ(ierr); PetscBool flag = PETSC_FALSE; PetscReal secs = -1; ierr = PetscOptionsHasName(0,"-sleep",&flag);CHKERRQ(ierr); ierr = PetscOptionsGetReal(0,"-sleep",&secs,0);CHKERRQ(ierr); if (flag) {ierr = PetscSleep(secs);CHKERRQ(ierr);} ierr = PetscFinalize();CHKERRQ(ierr); return 0; } ```