How can I fix this "Error using / Matrix dimensions must agree."

Matlab gives me an error that says "error using / matrix dimensions must agree." "error in Q_bc = (1/n) * (B/ (B + 2*h_bc)).*(h_bc.^(2/3)).*(S.^(1/2))"

how can I fix this can you help me? thank you.

% Step 1: Define the parameters and initial conditions.

B = 200; % River width (m)

n = 0.035; % Manning coefficient

S = 10^(-4); % Bottom slope

Q_eq = 800; % Equilibrium flow rate (m3/s)

h_eq = 4; % Equilibrium water depth (m)

h_basin = 6.4; % Basin water level to start filling (m)

A_basin = 5108; % Basin surface area (m2)

x_upstream = 450; % Location of boundary condition (km)

T = 6; % Period of sinusoidal wave (days)

h_wave = 4; % Height of sinusoidal wave (m)

% Step 2: Set up the numerical grid.

L = 400000; % Length of the river (m)

dx = 1000; % Grid spacing (m)

dt = 3600*24; % Time step (s)

x = 0:dx:L; % Spatial grid

t = 0:dt:T*24*3600; % Time grid

nx = length(x);

nt = length(t);

h = zeros(nx, nt); % Matrix to store water depths

h(:, 1) = h_eq; % Set initial condition as equilibrium depth

% Step 3: Apply the boundary condition.

h_bc = h_eq + h_wave*sin(2*pi*t/T); % Water level at the boundary

% Convert the boundary water levels to discharges using Manning equation

Q_bc = (1/n) * (B/ (B + 2*h_bc)).*(h_bc.^(2/3)).*(S^(1/2));

Answer 1

[Dyuman Joshi]

I assume you want to do element-wise division, use "./" for that

% Step 1: Define the parameters and initial conditions.
B = 200;        % River width (m)
n = 0.035;      % Manning coefficient
S = 10^(-4);    % Bottom slope
Q_eq = 800;     % Equilibrium flow rate (m3/s)
h_eq = 4;       % Equilibrium water depth (m)
h_basin = 6.4;  % Basin water level to start filling (m)
A_basin = 5108; % Basin surface area (m2)
x_upstream = 450;   % Location of boundary condition (km)
T = 6;              % Period of sinusoidal wave (days)
h_wave = 4;         % Height of sinusoidal wave (m)
% Step 2: Set up the numerical grid.
L = 400000;    % Length of the river (m)
dx = 1000;     % Grid spacing (m)
dt = 3600*24;  % Time step (s)
x = 0:dx:L;    % Spatial grid
t = 0:dt:T*24*3600; % Time grid
nx = length(x);
nt = length(t);
h = zeros(nx, nt); % Matrix to store water depths
h(:, 1) = h_eq; % Set initial condition as equilibrium depth
% Step 3: Apply the boundary condition.
h_bc = h_eq + h_wave*sin(2*pi*t/T); % Water level at the boundary
% Convert the boundary water levels to discharges using Manning equation
%                v here
Q_bc = (1/n) * (B./ (B + 2*h_bc)).*(h_bc.^(2/3)).*(S^(1/2))

Q_bc = 1×7

0.6923 0.6923 0.6923 0.6923 0.6923 0.6923 0.6923

Answer 2

[Sania Nizamani]

The last line should read as follows:

Q_bc = (1/n) * (B./ (B + 2*h_bc)).*(h_bc.^(2/3)).*(S^(1/2));

You had missed the dot there. You must have typed (B./ instead of (B/

I hope it helps.