the variable appears to change size every loop iteration

%(a)Write the following script to plot the magnetization curve.

clc

clear

If = [0 0.5 1.0 1.5 2.0 2.5];

Ea = [0 75 150 205 242 270];

Ra = 0.14;

RI = 2;

la = 100;

Ifield = linspace(0,2.5,100);

for n = 1:100

Ea_curve(n) = spline(If,Ea,lfield(n));

end

plot(Ifield, Ea_curve)

title ('Field current vs. Generated EMF')

xlabel('Field current [A]')

ylabel('Generated EMF [V]')

Answer 1

[Alan Stevens]

You don't need the loop:

If = [0 0.5 1.0 1.5 2.0 2.5];
Ea = [0 75 150 205 242 270];
Ra = 0.14;
RI = 2;
la = 100;
Ifield = linspace(0,2.5,100);
Ea_curve = spline(If,Ea,Ifield);
plot(Ifield, Ea_curve)
title ('Field current vs. Generated EMF')
xlabel('Field current [A]')
ylabel('Generated EMF [V]')

[Nisreen Aljumaili]

thank you so much:)

I am sorry i tried the same way with this code and did not use the loop but it did not work

clc

clear

If = [0 0.5 1.0 1.5 2.0 2.5];

Ea = [0 75 150 205 242 270];

Ra = 0.14

RI = 2;

Ifield = linspace(0,2.5,100);

for n = 1:100

Ea_curve(n) = spline(lf, Ea, Ifield(n));

la(n) = Ea_curve(n)/2;

Vt(n) = Ea_curve(n)-la(n)*Ra;

Pload(n) = Ea_curve(n)*la(n);

end

plot(Ifield, Vt)

title ('Field current vs. Terminal voltage')

xlabel('Field current [A]')

ylabel('Terminal voltage [V]')

[Alan Stevens]

If = [0 0.5 1.0 1.5 2.0 2.5];
Ea = [0 75 150 205 242 270];
Ra = 0.14;
RI = 2;
Ifield = linspace(0,2.5,100);
Ea_curve = spline(If, Ea, Ifield);  % If not lf
la = Ea_curve/2;
Vt = Ea_curve-la*Ra;
Pload = Ea_curve.*la;   % Notice the dot in .*
plot(Ifield, Vt)
title ('Field current vs. Terminal voltage')
xlabel('Field current [A]')
ylabel('Terminal voltage [V]')

Answer 2

[Image Analyst]

You're getting the warning because of this line

Ea_curve(n) = spline(If,Ea,lfield(n));

So every time you want to stuff a new number into the nth location of Ea_curve, it has to reallocation a new chunk of memory as big as the entire array, not just one 8 byte chunk for the additional element. To avoid the error you can preallocate Ea_curve with zeros before the loop

Ea_curve(n) = zeros(1, 100);
for n = 1 : 100