fix: ensure the largest grid to be accumulated

Note that idx1d array may not contain the index of the largest grid,
which is 10000. In this case, the reshape will complain about the
mismatched dimension.

mcxlab/examples/demo_polarized_photon.m

@@ -82,10 +82,9 @@
 % output 2D maps (100x100) for I Q U V
 ix=discretize(detphoton1.p(:,1),0:0.2:20);
 iy=discretize(detphoton1.p(:,2),0:0.2:20);
-idx1d=sub2ind([100,100],iy,ix);
 HIQUV1=zeros(4,100,100);
 for i=1:4
-    HIQUV1(i,:,:)=reshape(accumarray(idx1d,s2(:,i)),[100,100]);
+    HIQUV1(i,:,:)=accumarray([iy,ix],s2(:,i),[100,100]);
 end
 
 % plot
@@ -135,10 +134,9 @@
 % output 2D maps (100x100) for I Q U V
 ix=discretize(detphoton2.p(:,1),0:0.2:20);
 iy=discretize(detphoton2.p(:,2),0:0.2:20);
-idx1d=sub2ind([100,100],iy,ix);
 HIQUV2=zeros(4,100,100);
 for i=1:4
-    HIQUV2(i,:,:)=reshape(accumarray(idx1d,s2(:,i)),[100,100]);
+    HIQUV2(i,:,:)=accumarray([iy,ix],s2(:,i),[100,100]);
 end
 
 % plot