LogLog Plot is Blank

I am unable to plot anything on a loglog plot with this code:

%Paschen Curve Plotting for H2
p = 1.2; %Torr
d = 20; %cm
GamSE = 1;

%Constants
A = 4.8;
B = 136;
dM = 20*0.01; %Convert units to m

%For Graphing
NumG = B.*x;
DenG = log(A.*x) - log(log(1 + 1/GamSE));
y = (B.*x)/((log(A.*x) - log(log(1 + 1/GamSE)))*dM);

x = logspace(-1,4,50);

loglog(x,y)
hold on
grid on
xlabel('p*d (Torr-cm)')
ylabel('Eb (V/m)')
hold off

It's just blank. I have tried modfiying the limit of the logspace call since the equation should exponetially grow for x < 1 and this still didn't fix it. What am doing incorrectly here?

[Stephen23]

"What am doing incorrectly here?"

https://www.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html

Answer 1

[Star Strider]

Use element-wise division:

y = (B.*x)/((log(A.*x) - log(log(1 + 1/GamSE)))*dM);

↑ ← HERE

and it works!

%Paschen Curve Plotting for H2
p = 1.2; %Torr
d = 20; %cm
GamSE = 1;

%Constants
A = 4.8;
B = 136;
dM = 20*0.01; %Convert units to m
x = logspace(-1,4,50);

%For Graphing
NumG = B.*x;
DenG = log(A.*x) - log(log(1 + 1/GamSE));
y = (B.*x)./((log(A.*x) - log(log(1 + 1/GamSE)))*dM);



loglog(x,y)
hold on
grid on
xlabel('p*d (Torr-cm)')
ylabel('Eb (V/m)')
hold off

Warning: Negative data ignored

Wioth matrix division ratther than array division, ‘y’ is a scalar. Scalars only plot with markers, since a lline has to be defined by at least two (x,y) pairs.

Forgetting do to element-wise division is probably the most common problem I see here.

.

[John]

Thank you @Star Strider, I wasn't aware that I needed to do it for that division symbol too. I did notice that the original function was a scalar rather than an array but wasn't sure why.

[Star Strider]

As always, my pleasure!

Answer 2

[Alan Stevens]

Like this? (I've assumed you want log base 10 everywhere):

%Paschen Curve Plotting for H2
p = 1.2; %Torr
d = 20; %cm
GamSE = 1;

%Constants
A = 4.8;
B = 136;
dM = 20*0.01; %Convert units to m

%For Graphing
x = logspace(-1,4,50);

NumG = B.*x;
DenG = log10(A.*x) - log10(log10(1 + 1/GamSE));
y = (B.*x)./((log10(A.*x) - log10(log10(1 + 1/GamSE)))*dM);  % dot divide


loglog(x,y)
hold on
grid on
xlabel('p*d (Torr-cm)')
ylabel('Eb (V/m)')
hold off

[John]

Thank you for the answer @Alan Stevens! Wish I could accept more than one answer.