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Problem with ordinary differental equation

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fiza fiza
fiza fiza 2016 年 12 月 1 日
回答済み: Ghanim 2023 年 1 月 11 日
Good Afternoon,
I have a problem on how to solve differential equation which is dsdx and dxdPO2_rbc. This is the equation that I want to solve:
dPO2dt= (Qb*(O2_bloodin - O2_blood)+ (DO2_m * (PO2_g - PO2,b)))./ (Vb * (alpha_O2 + (cap_b * dsdx * dxdp))); %.... equation (1)
which:
a1= -8532;
a2= 2121;
a3= -67.07;
a4= 936000;
a5= -31350;
a6= 2396;
a7= -67.10;
T= 37;
r= 0.69;
H_rbc= 61*exp(-9);
ph_virt= -log(r*H_rbc);
PO2_rbc= 90 %mmHg;
pco2= 46 %mmhg;
I have problem with dsdx and dxdPO2, where
S(x)=(a1*x + a2*x^2 + a3*x^3 + x^4)/ (a4 + a5*x + a6*x^2 + a7*x^3 + x^4) %.......(equation 2)
x= PO2_rbc * (10^(0.024*(37-T) + 0.4*(ph_virt - 7.4)+ 0.06*(log(40/PCO2)))) %.........(equation 3)
I try to differentiate S with respect to x using 'diff', and differentiate x with respect to PO2_rbc, but the result is in symbolic (sym) form. Hence, it cannot be solved in equation (1).
Could somebody help me with this problem? I mean, should I use 'diff' to solve dSdx and dxdPO2_rbc, or another method?
Thanks..

採用された回答

Karan Gill
Karan Gill 2016 年 12 月 1 日
編集済み: Karan Gill 2017 年 10 月 17 日
I think what you're asking is how to go from symbolic to numeric form? Use the "subs" function to substitute symbolic values with numbers. Then convert the symbolic result to double using "double".
  3 件のコメント
Karan Gill
Karan Gill 2016 年 12 月 8 日
If you used "dsolve" so solve your problem symbolically, then why are you giving the solution from "dsolve" to "ode45". You already have the solution in double form. Just try to plot it using "plot" etc.
fiza fiza
fiza fiza 2017 年 1 月 9 日
編集済み: fiza fiza 2017 年 1 月 9 日
OK.. I changed to this code, and it works. Thanks... :-)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
syms x
S= ((a1*x) + (a2*(x^2)) + (a3*(x^3)) + (x^4))/ (a4 + a5*x + (a6*(x^2)) + (a7*(x^3)) + (x^4));
diff_S= jacobian(S,x);
diff_simple= simplify(diff_S);
eqn= Xa(8) * (10^(0.024*(37-T) + 0.4*(ph_virt - 7.4)+ 0.06*(log(40/Xa(3)))));
int_subs= subs(diff_simple,x,eqn);
h= double(int_subs);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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その他の回答 (1 件)

Ghanim
Ghanim 2023 年 1 月 11 日
d2y/dx^2+5y-4=0

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