MATLAB: How to obtain matrix with two symbolic equations with dsolve

differential equationsdsolve

clc, clear
a1=28*7*400;                        %%ft^2
po=40.6;                            %%psi







dpio=9;                           %%psi
qf=1525;                            %%gpm

qo=qf;
pp=16.4;                            %%psi
qp=1234;                            %%gpm
depr1=24.9;                         %%psi
delp=depr1-pp;                      %%psi
delpr2=18.2;                        %%psi
PH=360;                                     %%ft
lp=2.76*.264/(60)^2*14.5;                   %%gal/m*min^2/psi
k2=1.75*10^-4*60^1.67*14.5/264.172^1.67;     %%psi/(gal/min)^1.67
k3=2.27*10^-2;                                  %%(m^3/h)^.6/m^2
g=32.17;                            %%ft/s^2
rhoh20=62.4;                        %%lbs/ft^3
pf=rhoh20*g*PH*1.488*.000145;       %%psi
dpo=pf-po;                     %%psi
eqns=ro_cp_model(lp,qo,dpio,k3,k2,dpo);
function dpq=ro_cp_model(lp,qo,dpio,k3,k2,dpo)
syms jjw dp(x) Q(x)
eqns=[diff(Q,x,1)==-(lp(dp-qo*dpio/Q*exp(jjw/(k3*Q^.4))))*am, diff(dp,x,1)==-k2*Q];
conditions=[dp(0)==dpo Q(0)==qo];
dpq=vpa(dsolve(eqns,conditions));
end 
Error using symfun/subsindex (line 157)
Indexing values must be positive integers, logicals,
or symbolic variables.
Error in ro_cp_model (line 4)
eqns=[diff(Q,x,1)==-(lp(dp-qo*dpio/Q*exp(jjw/(k3*Q^.4))))*am,
diff(dp,x,1)==-k2*Q];
Error in mhlro (line 20)
eqns=ro_cp_model(lp,qo,dpio,k3,k2,dpo);
 
>>
I would like to show a matrix of the anwsers of the two diff. equations with the only uknown value beng jjw.

Best Answer

lp(dp-qo*dpio/Q*exp(jjw/(k3*Q^.4)))
You have requested variable lp indexed at expression dp-qo*dpio/Q*exp(jjw/(k3*Q^.4)) but that expression involves symbolic variables, and you can never index at a symbolic location.
MATLAB does not have implied multiplication in any context, not even inside the symbolic toolbox.
Related Question