Why do I keep getting "Unable to perform assignment because the indices on the left side are not compatible with the size of the right side." error?

This is my code:

function simulate_sscf()

% Set initial conditions and reaction time

initial_conditions = [30; 0; 0; 7.5; 3; 0]; % initial concentrations of cellulose, cellobiose, glucose, xylose, biomass and ethanol

tspan = [0 36]; % duration of simulation

[t, concentrations] = ode45(@rate_equation, tspan, initial_conditions);

% Plot the Results

plot(t, concentrations)

xlabel('Time (hr)')

ylabel('Concentration (g/L)')

legend('Cellulose','Cellobiose','Glucose','Xylose','Biomass', 'Ethanol');

end

function dxdt = rate_equation(~,x)

global k1r E1B Rs S0 K1IG K1IG2 G XY K1IX k2r E2B K2IG2 K2IG K2IX k3r E2F K3M K3IG K3IX K1ad E1TZ E1max K2ad E2TZ E2max

C = x(1); % Cellulose concentration

G2 = x(2); % Cellobiose concentration

SG = x(3); % Glucose concentration

SX = x(4); % Xylose concentration

X = x(5); % Biomass concentration

P = x(6); % Product concentration

% Define constants for Saccharification

% Substrate reactivity is an assumption based on Figure 2 of ref.paper

K1ad=0.4;

K2ad=0.1;

E1max=0.06;

E2max=0.01;

Ea=-5540;

k1r=22.3;

k2r=7.18;

k3r=285.5;

K1IG2=0.015;

K1IG=0.1;

K1IX=0.1;

K1IE=0.15;

K2IG2=132;

K2IG=0.04;

K2IX=0.2;

K3M=24.3;

K3IG=3.9;

K3IX=201;

XY=0;

Rs=1.987; % where C0 is the initial concentration of cellulose

R=1.987;

E1F=1/2*(-1/K1ad + E1TZ-E1max*C + sqrt((-1/K1ad + E1TZ - E1max*C)^2 + 4*E1TZ/K1ad));

E1B=(E1max*K1ad*E1F*C)/(1+K1ad*E1F);

E2F=1/2*(-1/K2ad + E2TZ - E2max*C + sqrt((-1/K2ad + E2TZ - E2max*C)^2 + 4*E2TZ/K2ad));

E2B=(E2max*K2ad*E2F*C)/(1+K2ad*E2F);

% Define constants for glucose fermentation

mu_mG = 0.662; % Maximum specific growth rate in glucose fermentation

KsG = 0.565; % Monod constant, for growth on glucose

KiG = 283.7; % Inhibition constant, for growth on glucose

betaG = 1.29; % constants in product inhibition model in glucose fermentation

PmG = 95.4; % Ethanol concentration above which cells don't grow in glucose

vmG = 2.005; % Maximum specific rate of glucose formation

Ks2G = 1.342; % Monod constant, for product formation from glucose

Ki2G = 4890; % Inhibition constant, for product formation from glucose

gammaG = 1.42; % Maximum specific rate of glucose formation

Pm2G = 103; % Ethanol concentration above which cells do not produce ethanol in glucose fermentation

YEtG_G = 0.470; % product yield constant (g-ethanol/g-glucose)

YXG_G = 0.115; % cell yield constant from glucose (g-cells/g-substrate)

mG = 0.097; % maintenance coefficient in glucose fermentation

% Define constants for xylose fermentation

mu_mX = 0.190; % Maximum specific growth rate in xylose fermentation

KsX = 3.4; % Monod constant, for growth on xylose

KiX = 18.1; % Inhibition constant, for growth on xylose

betaX = 1.036; % constant in product inhibition model in xylose fermentation

PmX = 59.04; % Ethanol concentration above which cells don't grow in xylose

vmX = 0.250; % Maximum specific rate of xylose formation

Ks2X = 3.4; % Monod constant, for product formation from glucose

Ki2X = 81.3; % Inhibition constant, for product formation from glucose

gammaX = 0.608; % Maximum specific rate of glucose formation

Pm2X = 60.2; % Ethanol concentration above which cells do not produce ethanol in glucose fermentation

YEtX_X = 0.400; % product yield constant (g-ethanol/g-xylose)

YXX_X = 0.162; % cell yield constant from xylose (g-cells/g-substrate)

mX = 0.067; % maintenance coefficient in xylose fermentation

n = 0.5; % weighting factor for glucose consumption

% Define rates of reaction

% cellulose to cellobiose

r(1)=(k1r*E1B*Rs*C)/(1+(G2/K1IG2)+(SG/K1IG)+(SX/K1IX)+(P/K1IE));

% cellulose to glucose

r(2)=(k2r*(E1B+E2B)*Rs*C)/(1+(G2/K2IG2)+(SG/K2IG)+(SX/K2IX));

% cellobiose to glucose

r(3)=(k3r*E2F*G2)/K3M*(1+(SG/K3IG)+(SX/K3IX))+G2;

% Biomass Production from Glucose

mu_G = mu_mG * (SG / (KsG + SG + (SG^2/KiG))) * (1 - (P/PmG)^betaG);

% Biomass Production from Xylose

mu_X = mu_mX * (SX / (KsX + SX + (SX^2/KiX))) * (1 - (P/PmX)^betaX);

% Total Biomass Production from Both

mu_T = n*mu_G + (1-n)*mu_X;

% Ethanol Formation from Glucose

vG = vmG * (SG / (Ks2G + SG + (SG^2/Ki2G))) * (1 - (P/Pm2G)^gammaG);

% Ethanol Formation from Xylose

vX = vmX * (SX / (Ks2X + SX + (SX^2/Ki2X))) * (1 - (P/Pm2X)^gammaX);

% Total Ethanol Formation from both

vT = vG + vX;

% Define rate equations

dCdt = -r(1)-r(2); % Rate of change of cellulose

dG2dt = 1.056*r(1)-r(3); % Rate of change of cellobiose

dXdt = mu_T * X; % Rate of change of biomass

dPdt = vT * X; % Rate of change of product

dSGdt = 1.111*r(2)+1.053*r(3)-(1/YEtG_G) * vG * X; % Rate of change of glucose in SSCF

dSXdt = -(1/YEtX_X) * vX * X; % Rate of change of xylose in SSCF

dxdt = [dCdt; dG2dt; dSGdt; dSXdt; dXdt; dPdt];

end

Any help will be greatly appreciated!

Answer 1

[Sai Teja G]

Hi Debbie,

The error message "Unable to perform assignment because the indices on the left side are not compatible with the size of the right side" suggests that there's a discrepancy in the array or matrix dimensions that you're attempting to equate.

It appears that in the lines where you're calculating `r(1)`, `r(2)`, and `r(3)`, the expected output should be scalar values. However, it seems that the variables `E1B`, `E2F`, and `E2B` are not scalar values as they should be. Instead, they are currently empty arrays, denoted by `[]`, which is causing the error.

Could you please review your code to ensure that `E1B`, `E2B`, and `E2F` are being correctly calculated as scalar values? Once you make the necessary adjustments to these variables, the error should be resolved.

Hope it helps!