int dataSize = 11;
int imgSize = 200;
vec3 orig = [0.0, 0.0, 5.0];
vec3 cVec = [0.0, 1.0, 0.0];
vec3 rVec = [1.0, 0.0, 0.0];
image(3)[] img = load("../data/zimg11.nrrd");
field#2(3)[] F = img ⊛ bspln3;

strand RayCast (int row, int col)
{
    real rr = lerp(-0.5, real(dataSize)-0.5, -0.5, real(row), real(imgSize)-0.5);
    real cc = lerp(-0.5, real(dataSize)-0.5, -0.5, real(col), real(imgSize)-0.5);
    vec3 pos = orig + rr*rVec + cc*cVec;
    output real val = 0.0; 

    update
    {
        if (inside (pos,F)) {
	    tensor[3,3] H = ∇(∇F)@pos;
            // HEY BUG
            // /usr/bin/gcc -std=gnu99 -m64 -c -NDEBUG -g -O2 -Wformat -Wreturn-type -Wuninitialized -I/Users/gk/diderot/diderot/pure-cfg/src/include -I/Users/gk/diderot/teem/arch/darwin.32/include zslice-hess3.c
            // zslice-hess3.c: In function ‘RayCast_update’:
            // zslice-hess3.c:607: error: too few arguments to function ‘mulMat3x3Mat3x3f’
            // uncaught exception Fail [Fail: error compiling/linking]
            //   raised at c-target/c-target.sml:706.17-706.47
	    val = trace(H•H);
	}
        stabilize;
    }
}

initially [ RayCast(r, c) | r in 0..(imgSize-1), c in 0..(imgSize-1) ];