In MATLAB, you can create a model for a resistor with resistance that varies with time or temperature by defining a function that calculates the resistance based on the desired variation. You can use mathematical equations or empirical data to model the resistance variation.

The Code can be like:

function resistance = variable_resistor(time_or_temperature)

% Define the equation or algorithm for resistance variation

% For example, you could use a linear or exponential function

% based on time or temperature

% resistance = some_function(time_or_temperature);

% Example: Resistance increases linearly with time

resistance = initial_resistance + time_or_temperature * time_variation_rate;

end

You would need to replace some_function with the appropriate mathematical expression or algorithm that describes how the resistance varies with time or temperature. You can also replace initial_resistance and time_variation_rate with appropriate values or parameters depending on your specific scenario.

Once you have defined the function variable_resistor, you can use it in your MATLAB code by passing the desired time or temperature value as input and obtaining the corresponding resistance value as output.

If you're looking for a ready-made MATLAB element or toolbox that provides such functionality, you might want to explore specialized toolboxes for circuit simulation or physical modeling. These toolboxes often include components with variable parameters that can be specified as functions of time, temperature, or other variables. Some examples include Simscape Electrical and Simscape Power Systems.

Additionally, MATLAB also offers optimization and curve fitting tools that can help you derive mathematical models for resistance variation based on empirical data. You can use these tools to fit experimental data to mathematical equations and obtain a model that describes the variation accurately.

I am not sure if Simulink has such resistor models already built in it but below is a simple Matlab script that can be used to model such a resistor whose resistance value varies with time. I have used the sine function to model the transient variation. You can define anything as per your needs.

% Define time vector

t = linspace(0, 10, 1000); % Adjust time range and resolution as needed

% Define a function for temperature variation with time (customize as needed)

temperature = 25 + 10 * sin(2 * pi * 0.05 * t);

% Define a function for resistance variation with time and temperature (customize as needed)

resistance = 10 + 5 * sin(2 * pi * 0.1 * t) + 0.1 * (temperature - 25);

figure;

plot(t, temperature, 'LineWidth', 2);

xlabel('Time (s)');

ylabel('Temperature (°C)');

title('Resistor Temperature vs Time');

figure;

plot(t, resistance, 'LineWidth', 2);

xlabel('Time (s)');

ylabel('Resistance (\Omega)');

title('Variable Resistor: Resistance vs Time');