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Why my result is 0×1 empty double column vector

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arham zakki edelo
arham zakki edelo 2019-5-18
回答： Walter Roberson 2019-5-18
function[u_g] = viscosity(Pm) % viscosity() calculates viscosity of the gas at given reservoir % temperature and pressure.
M_air=[28.96;29;29.56;30;31;31.86;32;32.3;33;33.50];
Avg_Mol_Wt= [25.48;26;26.12;26.79;27;27.60;28;29;29.40;30];
spgr=Avg_Mol_Wt.\M_air;
Pm=[3800;3850;3400;3450;3500;3550;3600;3650;3700;3750]; %initial reservoir pressure
T=[660;680;720;740;760;780;800;820;840;860]; %Reservoir Temperature= 660 deg R (Literature)
u_uncorrected = ((1.709 * (10^(-5)-(2.062*10^(-6)*spgr))).*(T-460))+((8.118*10^(-3))-(6.15*10^(-3)*log10(spgr)));
yCO2 = 0.03;
yN2 = 0.02;
yH2S = 0.01;
u_CO2 = (yCO2*(((9.08*10^(-3))*(log10(spgr)))+ (6.24*10^(-3))));
u_N2 = (yN2*((8.48*10^(-3)*log10(spgr))+ (9.59*10^(-3))));
u_H2S = (yH2S*((8.49*10^(-3)*log10(spgr))+ (3.73*10^(-3))));
u1 = u_uncorrected + u_CO2 + u_N2 + u_H2S ;
Tpc = 168 + (325 * spgr) -(12.5*(spgr.^2));
Ppc = 677 + (15*spgr) -(37.5*(spgr.^2));
Tpr = T/Tpc;
Ppr = Pm/Ppc;
% Constants for viscosity relation
a0 = -2.4621182;
a1 = 2.970547414;
a2 = -0.286264054;
a3 = 0.008054205;
a4 = 2.80860949;
a5 = -3.49803305;
a6 = 0.36037302;
a7 = -0.01044324;
a8 = -0.793385648;
a9 = 1.39643306;
a10 = -0.149144925;
a11 = 0.004410155;
a12 = 0.083938718;
a13 = -0.186408848;
a14 =0.020336788;
a15 = -0.000609579;
syms ug;
con = a0+(a1.*Ppr)+(a2.*(Ppr.^2))+ (a3.*(Ppr.^3)) +(Tpr.*(a4+(a5.*Ppr)+(a6.*Ppr.^2)+(a7.*Ppr.^3)))+((Tpr.^2)*(a8+(a9.*Ppr)+(a10.*Ppr.^2)+(a11.*Ppr.^3)))+((Tpr.^3)*(a12+(a13.*Ppr)+(a14.*Ppr.^2)+(a15.*Ppr.^3)));
eqn = ((Tpr.*ug) == u1.*exp(con));
temp = solve(eqn,'ug');
u_g = double(temp);
end
results
>> viscosity
Warning: Do not specify equations and variables as
character vectors. Instead, create symbolic variables
with syms.
> In solve>getEqns (line 446)
In solve (line 226)
In viscosity (line 40)
ans =
0×1 empty double column vector

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回答（2 个）

John D'Errico
John D'Errico 2019-5-18
编辑：John D'Errico 2019-5-18
Um, LOOK AT WHAT YOU DID?
eqn
eqn =
[ 0 == 5780664229092589/18446744073709551616, 0 == 5780664229092589/18446744073709551616, 0 == 5780664229092589/18446744073709551616, 0 == 5780664229092589/18446744073709551616, 0 == 5780664229092589/18446744073709551616, (5645467684136263*ug)/4503599627370496 == 3053705270954071/288230376151711744, 0 == 5780664229092589/18446744073709551616, 0 == 4586793404289899/8796093022208, 0 == 5780664229092589/18446744073709551616, 0 == 5780664229092589/18446744073709551616]
[ 0 == 5600019709277477/18446744073709551616, 0 == 5600019709277477/18446744073709551616, 0 == 5600019709277477/18446744073709551616, 0 == 5600019709277477/18446744073709551616, 0 == 5600019709277477/18446744073709551616, (5816542462443423*ug)/4503599627370496 == 822835767405345/72057594037927936, 0 == 5600019709277477/18446744073709551616, 0 == 3047385662287835/4398046511104, 0 == 5600019709277477/18446744073709551616, 0 == 5600019709277477/18446744073709551616]
[ 0 == 2572630575198711/9223372036854775808, 0 == 2572630575198711/9223372036854775808, 0 == 2572630575198711/9223372036854775808, 0 == 2572630575198711/9223372036854775808, 0 == 2572630575198711/9223372036854775808, (3079346009528871*ug)/2251799813685248 == 7486683279545443/576460752303423488, 0 == 2572630575198711/9223372036854775808, 0 == 1741669557772335/2199023255552, 0 == 2572630575198711/9223372036854775808, 0 == 2572630575198711/9223372036854775808]
[ 0 == 2472319987732461/9223372036854775808, 0 == 2472319987732461/9223372036854775808, 0 == 2472319987732461/9223372036854775808, 0 == 2472319987732461/9223372036854775808, 0 == 2472319987732461/9223372036854775808, (6329766797364901*ug)/4503599627370496 == 4002404158088997/288230376151711744, 0 == 2472319987732461/9223372036854775808, 0 == 4733878050545925/4398046511104, 0 == 2472319987732461/9223372036854775808, 0 == 2472319987732461/9223372036854775808]
[ 0 == 2346687901508061/9223372036854775808, 0 == 2346687901508061/9223372036854775808, 0 == 2346687901508061/9223372036854775808, 0 == 2346687901508061/9223372036854775808, 0 == 2346687901508061/9223372036854775808, (6500841575672061*ug)/4503599627370496 == 8453485532814763/576460752303423488, 0 == 2346687901508061/9223372036854775808, 0 == 1593573526385771/1099511627776, 0 == 2346687901508061/9223372036854775808, 0 == 2346687901508061/9223372036854775808]
[ 0 == 8946768155106723/36893488147419103232, 0 == 8946768155106723/36893488147419103232, 0 == 8946768155106723/36893488147419103232, 0 == 8946768155106723/36893488147419103232, 0 == 8946768155106723/36893488147419103232, (1667979088494805*ug)/1125899906842624 == 8964393129251763/576460752303423488, 0 == 8946768155106723/36893488147419103232, 0 == 1080598422980285/549755813888, 0 == 8946768155106723/36893488147419103232, 0 == 8946768155106723/36893488147419103232]
[ 0 == 1069123269945641/4611686018427387904, 0 == 1069123269945641/4611686018427387904, 0 == 1069123269945641/4611686018427387904, 0 == 1069123269945641/4611686018427387904, 0 == 1069123269945641/4611686018427387904, (1710747783071595*ug)/1125899906842624 == 4767346375255051/288230376151711744, 0 == 1069123269945641/4611686018427387904, 0 == 2948226993291101/1099511627776, 0 == 1069123269945641/4611686018427387904, 0 == 1069123269945641/4611686018427387904]
[ 0 == 4100813596974095/18446744073709551616, 0 == 4100813596974095/18446744073709551616, 0 == 4100813596974095/18446744073709551616, 0 == 4100813596974095/18446744073709551616, 0 == 4100813596974095/18446744073709551616, (7014065910593539*ug)/4503599627370496 == 317887318073797/18014398509481984, 0 == 4100813596974095/18446744073709551616, 0 == 4045185938083311/1099511627776, 0 == 4100813596974095/18446744073709551616, 0 == 4100813596974095/18446744073709551616]
[ 0 == 7774278768879437/36893488147419103232, 0 == 7774278768879437/36893488147419103232, 0 == 7774278768879437/36893488147419103232, 0 == 7774278768879437/36893488147419103232, 0 == 7774278768879437/36893488147419103232, (7185140688900699*ug)/4503599627370496 == 670498029164941/36028797018963968, 0 == 7774278768879437/36893488147419103232, 0 == 2750305037577659/549755813888, 0 == 7774278768879437/36893488147419103232, 0 == 7774278768879437/36893488147419103232]
[ 0 == 1846563996020195/9223372036854775808, 0 == 1846563996020195/9223372036854775808, 0 == 1846563996020195/9223372036854775808, 0 == 1846563996020195/9223372036854775808, 0 == 1846563996020195/9223372036854775808, (3678107733603929*ug)/2251799813685248 == 354377367836401/18014398509481984, 0 == 1846563996020195/9223372036854775808, 0 == 7515208335023383/1099511627776, 0 == 1846563996020195/9223372036854775808, 0 == 1846563996020195/9223372036854775808]
So, most of that mess is of a form like this:
eqn(1)
ans =
0 == 5780664229092589/18446744073709551616
Which value of ug will satisfy that EXACTLY? Yeah, right. It looks like there will never be a solution to what you are doing. Not that we are given a hint as to what you really need to do, which is probably not what you actually wrote code to do since that system of equations is meaningless.
So, why is your result an empty vector? Because there is no solution to what you posed.
Walter Roberson
Walter Roberson 2019-5-18
function[u_g] = viscosity(Pm) % viscosity() calculates viscosity of the gas at given reservoir % temperature and pressure.
M_air=[28.96;29;29.56;30;31;31.86;32;32.3;33;33.50];
Avg_Mol_Wt= [25.48;26;26.12;26.79;27;27.60;28;29;29.40;30];
spgr=Avg_Mol_Wt.\M_air;
Pm=[3800;3850;3400;3450;3500;3550;3600;3650;3700;3750]; %initial reservoir pressure
T=[660;680;720;740;760;780;800;820;840;860]; %Reservoir Temperature= 660 deg R (Literature)
u_uncorrected = ((1.709 * (10^(-5)-(2.062*10^(-6)*spgr))).*(T-460))+((8.118*10^(-3))-(6.15*10^(-3)*log10(spgr)));
yCO2 = 0.03;
yN2 = 0.02;
yH2S = 0.01;
u_CO2 = (yCO2*(((9.08*10^(-3))*(log10(spgr)))+ (6.24*10^(-3))));
u_N2 = (yN2*((8.48*10^(-3)*log10(spgr))+ (9.59*10^(-3))));
u_H2S = (yH2S*((8.49*10^(-3)*log10(spgr))+ (3.73*10^(-3))));
u1 = u_uncorrected + u_CO2 + u_N2 + u_H2S ;
Tpc = 168 + (325 * spgr) -(12.5*(spgr.^2));
Ppc = 677 + (15*spgr) -(37.5*(spgr.^2));
Tpr = T./Tpc; %CHANGED
Ppr = Pm./Ppc; %CHANGED
% Constants for viscosity relation
a0 = -2.4621182;
a1 = 2.970547414;
a2 = -0.286264054;
a3 = 0.008054205;
a4 = 2.80860949;
a5 = -3.49803305;
a6 = 0.36037302;
a7 = -0.01044324;
a8 = -0.793385648;
a9 = 1.39643306;
a10 = -0.149144925;
a11 = 0.004410155;
a12 = 0.083938718;
a13 = -0.186408848;
a14 =0.020336788;
a15 = -0.000609579;
syms ug;
con = a0+(a1.*Ppr)+(a2.*(Ppr.^2))+ (a3.*(Ppr.^3)) +(Tpr.*(a4+(a5.*Ppr)+(a6.*Ppr.^2)+(a7.*Ppr.^3)))+((Tpr.^2).*(a8+(a9.*Ppr)+(a10.*Ppr.^2)+(a11.*Ppr.^3)))+((Tpr.^3).*(a12+(a13.*Ppr)+(a14.*Ppr.^2)+(a15.*Ppr.^3))); %CHANGED IN TWO PLACES
eqn = ((Tpr.*ug) == u1.*exp(con));
temp = solve(eqn,'ug');
u_g = double(temp);
end
This will still not work, but it will get you to the much more compact
eqn =
(5702507353183325*ug)/4503599627370496 == 7212478526205445/144115188075855872
(2973544911973051*ug)/2251799813685248 == 433318337191181/9007199254740992
(6238234906800469*ug)/4503599627370496 == 1518433413966557/36028797018963968
(1613828264998639*ug)/1125899906842624 == 5989232554701665/144115188075855872
(6523595956302411*ug)/4503599627370496 == 3031307013761477/72057594037927936
(1667979088494805*ug)/1125899906842624 == 6063175485720917/144115188075855872
(1225*ug)/801 == 6021374973680469/144115188075855872
(7178082536150291*ug)/4503599627370496 == 2979923091249657/72057594037927936
(3658295761408275*ug)/2251799813685248 == 3003315655091799/72057594037927936
(49536*ug)/29683 == 754534745967413/18014398509481984
This can be analyzed in a least-squared sense to get a best-fit ug of about 0.028997375328324588909163169559149

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