Question: plots from a loop

in this program, i wuld like to plot R against a, the assign function does not work, can any one help me please????

result:=[]:

omega:=fsolve(subs(Pr= 0.025,subs(Pr[m]= 0, 10000*Pr^2*(Pr^2*(Pr-1)*(1+a^2/Pi^2)^2+10*Pr^2*(Pr+Pr[m])+Pr[m]^2*omega_1*(Pr-1))/((1+a^2/Pi^2)*(omega_1*(1+a^2/Pi^2)^2*(Pr+Pr*Pr[m])^2+(Pr^2*(1+a^2/Pi^2)^2-Pr[m]*omega_1+10*Pr^2)^2))+10*Pr^2*(Pr-Pr[m])/(Pr[m]^2*omega_1+Pr^2*(1+a^2/Pi^2)^2)+(1+Pr))),omega_1):
R:=(subs(Pr = 0.025, subs(Pr[m] = 0, (1+a^2/Pi^2)*Pi^2*((1+a^2/Pi^2)^2-omega/Pr+10*(omega*Pr*Pr[m]+Pr^2*(1+a^2/Pi^2)^2)/(Pr[m]^2*omega+Pr^2*(1+a^2/Pi^2)^2)+10000*Pr*((Pr^2*(1+a^2/Pi^2)^2-Pr[m]*omega+10*Pr^2)*(Pr*(1+a^2/Pi^2)^2-Pr[m]*omega)+omega*(1+a^2/Pi^2)^2*(Pr+Pr[m])*(Pr+Pr*Pr[m]))/((1+a^2/Pi^2)*(omega*(1+a^2/Pi^2)^2*(Pr+Pr*Pr[m])^2+(Pr^2*(1+a^2/Pi^2)^2-Pr[m]*omega+10*Pr^2)^2)))/a^2))*Pi^4):
for a from 4.56 to 7.56 do;
assign('result',[op(result),[a,R]]);
od;
plots:-pointplot(result);