Why am I getting "Arrays have incompatible sizes for the operation." error message?

>> % Circuit parameters
>> C = 15e-6; % capacitance (F)
>> L = 240e3; % inductance (H)
>> vm = 24; % source voltage amplitude (V)
>> 
>> 
>> % Range of frequencies and resistances
>> f = 60:1:110; % driving frequency (Hz)
>> R = 10:1:40; % resistance (ohms)
>> 
>> 
>> % Calculate amplitude of current
>> wd = 2*pi*f;
>> I = vm ./ sqrt(R.^2 + (wd*L - 1./(wd*C)).^2);
Arrays have incompatible sizes for this operation.

Related documentation
 
>> 

Answer 1

[Image Analyst]

% Circuit parameters
C = 15e-6; % capacitance (F)
L = 240e3; % inductance (H)
vm = 24; % source voltage amplitude (V)

% Range of frequencies and resistances
f = 60:1:110; % driving frequency (Hz)
R = 10:1:40; % resistance (ohms)
% Calculate amplitude of current
wd = 2*pi*f;
whos R

  Name      Size            Bytes  Class     Attributes

  R         1x31              248  double              

whos wd

  Name      Size            Bytes  Class     Attributes

  wd        1x51              408  double              

I = vm ./ sqrt(R.^2 + (wd*L - 1./(wd*C)).^2);

Arrays have incompatible sizes for this operation.

So R has 31 and wd has 51 elements so they can't be added together. Try using linspace to make sure they have the same number of elements.

% Circuit parameters
C = 15e-6; % capacitance (F)
L = 240e3; % inductance (H)
vm = 24; % source voltage amplitude (V)
% Range of frequencies and resistances
numElements = 51;
f = linspace(60,  110, numElements); % driving frequency (Hz)
R = linspace(10, 40, numElements); % resistance (ohms)
% Calculate amplitude of current
wd = 2*pi*f;
whos R
whos wd
I = vm ./ sqrt(R.^2 + (wd*L - 1./(wd*C)).^2);
plot(I, 'b.-', 'LineWidth', 2, 'MarkerSize', 20)
grid on;
xlabel('Index');
ylabel('I')