Im trying to solve an equation that have variable on left and right side
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Hamid Hamdi
am 23 Mai 2020
Kommentiert: Torsten
am 22 Aug. 2023
How do I solve this equation? I'm giving the important information also.
depth= 1385.33
por=0.153
Qv=0.980
B=3200
Rw=0.265
m=1.86
n=2.2
Rt=4.05
Sw=(Rw/((por^m)*Rt*(1+(B*Qv*Rw)/Sw)))^(1/n)
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John D'Errico
am 23 Mai 2020
Bearbeitet: John D'Errico
am 23 Mai 2020
How is depth relevant to anything here? It does not appear in the expression. Maybe I'm just not thinking very "deeply" today.
If Sw appears on both sides of the equality, surely you can subtract Sw? Just move everything to the same side. WTP?
por=0.153;
Qv=0.980;
B=3200;
Rw=0.265;
m=1.86;
n=2.2;
Rt=4.05;
fun = @(Sw) Sw - (Rw./((por^m)*Rt*(1+(B*Qv*Rw)./Sw))).^(1/n);
Note that for Sw <= 0, you either have a divide by zero at Sw == 0, or a complex result. So If any real solution exists, it must be for positive Sw.
Also note the use of ./ and .^ where necessary in fun. Does a solution exist? PLOT IT!
fplot(fun,[0,0.01])
yline(0);
It looks like a positive solution exists near 0.007.
[Swsol,fval] = fzero(fun,0.007)
Swsol =
0.00698017018548943
fval =
8.67361737988404e-19
We could also do this using symbolic tools. No analytical solution will exist because of the non-integer power.
syms Sw
vpasolve(fun(Sw))
ans =
0.006980170185489425081287353
No other positive root will exist. That should be not too difficult to prove.
2 Kommentare
Walter Roberson
am 28 Mai 2020
If this is a fitting process to determine the optimal Sw, then you would use different code.
You indicate that you have multiple Rt values; for a fitting you would also need multiple values of some other variable -- you need one more more independent variables and one or more dependent variables.
Weitere Antworten (3)
Ameer Hamza
am 23 Mai 2020
Bearbeitet: Ameer Hamza
am 23 Mai 2020
This is one of the methods
syms Sw
depth= 1385.33;
por=0.153;
Qv=0.980;
B=3200;
Rw=0.265;
m=1.86;
n=2.2;
Rt=4.05;
eq = Sw==(Rw/((por^m)*Rt*(1+(B*Qv*Rw)/Sw)))^(1/n);
sol = vpasolve(eq, Sw)
Walter Roberson
am 23 Mai 2020
depth= 1385.33
por=0.153
Qv=0.980
B=3200
Rw=0.265
m=1.86
n=2.2
Rt=4.05
F = @(Sw) (Sw) - ((Rw/((por^m)*Rt*(1+(B*Qv*Rw)/Sw)))^(1/n));
Sw = fsolve(F, 1.234)
2 Kommentare
N Sudharshan
am 22 Aug. 2023
Bearbeitet: Torsten
am 22 Aug. 2023
clear all %% solve for SN %%
Z=-1.282;
S=0.5;
PSI=1.9;
M=1000;
W=1000000;
syms SN
eqn = log10(W)==Z*S+9.36*log10(SN+1)-0.20+((log10(PSI/(4.2-1.5)))/(0.40+(1094/(SN+1)^5.19)))+2.32*log10(M)-8.07
solve(eqn)
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