我使用pdetool box求解对流 - 扩散方程。如果c和1，则如何使扩散系数y>0.03为0.2。感谢
c = 1;
a = 1;
f = 0
d = 1; xmin=0;xmax=0.575;ymin=0;ymax=0.05315;ymax2=0.066;
gdm = [3;4;xmin;xmax;xmax;xmin;ymax;ymax2;ymin;ymin];
g = decsg(gdm, 'S1', ('S1')');
hmax = .1; % element size
[p, e, t] = initmesh(g, 'Hmax', hmax);
[p,e,t] = refinemesh(g,p,e,t);
[p,e,t] = refinemesh(g,p,e,t);
[p,e,t] = refinemesh(g,p,e,t);
[p,e,t] = refinemesh(g,p,e,t);
[p,e,t] = refinemesh(g,p,e,t);
numberOfPDE = 1;
pb = pde(numberOfPDE);
% Create a geometry entity
pg = pdeGeometryFromEdges(g);
bc1 = pdeBoundaryConditions(pg.Edges(1),'u',100);
bc2 = pdeBoundaryConditions(pg.Edges(2),'u',66);
bc3 = pdeBoundaryConditions(pg.Edges(3),'u',11);
bc4 = pdeBoundaryConditions(pg.Edges(4),'g',0);
pb.BoundaryConditions = [bc1,bc2,bc3,bc4];
u = pdenonlin(pb,p,e,t,c,a,f, 'jacobian', 'lumped');
figure;
hold on
pdeplot(p, e, t, 'xydata', u, 'contour', 'off', 'colormap', 'jet(99)');
title 'chemical Diffusion, Steady State Solution'
xlabel 'X-coordinate, cm'
ylabel 'Y-coordinate, cm'