没什么矩阵B没有值，新手求解答，求修改！！！

clc,clear
load data.txt
[m,n]=size(data)
A=data;
B=[]
syms a b
for a=1:m
    for b=1:n
        if A(a,b)>0&&A(a,b)<50;
            B(a,b)=(A(a,b)-0)*50/50+0
            B(a,b)=(A(a,b)-0)*50/40+0
            B(a,b)=(A(a,b)-0)*50/50+0
            B(a,b)=(A(a,b)-0)*50/2+0
            B(a,b)=(A(a,b)-0)*50/35+0
        elseif A(a,b)>51&&A(a,b)<100;
                B(a,b)=(A(a,b)-51)*50/100+50
                B(a,b)=(A(a,b)-51)*50/40+40
                B(a,b)=(A(a,b)-51)*50/100+50
                B(a,b)=(A(a,b)-51)*50/2+2
                B(a,b)=(A(a,b)-51)*50/40+35% (10<t<20)
        elseif A(a,b)>101&&A(a,b)<150;
                B(a,b)=(A(a,b)-101)*50/325+150
                B(a,b)=(A(a,b)-101)*50/100+80
                B(a,b)=(A(a,b)-101)*50/100+150
                B(a,b)=(A(a,b)-101)*50/10+4
                B(a,b)=(A(a,b)-101)*50/40+75 %(20<t<30)
        elseif A(a,b)>151&&A(a,b)<200;
                B(a,b)=(A(a,b)-151)*50/325+475
                B(a,b)=(A(a,b)-151)*50/100+180
                B(a,b)=(A(a,b)-151)*50/100+250
                B(a,b)=(A(a,b)-151)*50/10+14
                B(a,b)=(A(a,b)-151)*50/35+115 %(30<t<40)
        elseif A(a,b)>201&&A(a,b)<300;
                    B(a,b)=(A(a,b)-201)*100/800+800
                    B(a,b)=(A(a,b)-201)*100/100+280
                    B(a,b)=(A(a,b)-201)*100/100+350
                    B(a,b)=(A(a,b)-201)*100/10+24
                    B(a,b)=(A(a,b)-201)*100/35+150 %(40<t<50)
        elseif A(a,b)>301&&A(a,b)<400;
                        B(a,b)=(A(a,b)-301)*100/500+1600
                        B(a,b)=(A(a,b)-301)*100/185+565
                        B(a,b)=(A(a,b)-301)*100/80+420
                        B(a,b)=(A(a,b)-301)*100/12+36
                        B(a,b)=(A(a,b)-301)*100/100+250 %(50<t<60)
                    else A(a,b)>401&&A(a,b)<500;
                            B(a,b)=(A(a,b)-301)*100/500+2100
                            B(a,b)=(A(a,b)-301)*100/185+750
                            B(a,b)=(A(a,b)-301)*100/80+500
                            B(a,b)=(A(a,b)-301)*100/12+48
                            B(a,b)=(A(a,b)-301)*100/100+350