Why do I keep getting "Error using plot Invalid data argument."

%Inputs
prompt1 = 'What is Tc?'
Tc = input(prompt1)          % In degrees F
k = 0.342;
Prompt2 = 'What is Tr?'
Tr = input(Prompt2);  % In degrees F
Prompt3 = 'What is Ti?'
Ti = input(Prompt3);  % In degrees F
t = -1/k.*log((Tc-Tr)/(Ti-Tr))  % Equation for amount of time taken
time = linspace(0,t*2)       % Time vector
Tc = Tr + (Ti - Tr)*exp(-k*t)   % Equation for fridge temp
plot(time,Tc, 'r', 'd')

Answer 1

[Voss]

Linespec (style, color, marker) should be specified as a single argument:

plot(time,Tc, 'rd')

[Walter Roberson]

Unless, that is, you use name-value pairs, such as

plot(time, Tc, 'Color', 'r', 'Marker', 'd')