Why am I getting invalid expression?

clear; clc
h = 34.869 ;
c = 13.679 ;
J2eV = 0.845 ;
counter = 0 ;
for lambda = 800:6:854
    counter = counter + 1 ;
    Lambda(counter) = lambda ;
    E(counter) = ((h * c) / lambda) / J2eV ;
    if ((E > 0.673 && (E < 0.678))
       disp('Energy in eV')
    end
end
E 
Lambda

Answer 1

[drummer]

You should declare Lambda and E as you made for counter.

You also had some flaws in the if condition (a missing parenthesis, and declare the indexes to E)

I made a quick review on the code, and I did not check whether it is optimized or not.

It follows below. =)

Cheers

clear; clc
h = 34.869 ;
c = 13.679 ;
J2eV = 0.845 ;
counter = 0 ;
Lambda = zeros; % declare as zeros
E = zeros;      % declare as zeros

for lambda = 800:6:854
    counter = counter + 1 ;
    Lambda(counter) = lambda ;
    E(counter) = ((h * c) / lambda) / J2eV ;
    if ((E(counter) > 0.673) && (E(counter) < 0.678)) % missing parenthesis and insert indexes to E
       disp('Energy in eV')
    end
end
E 
Lambda

[madhan ravi]

What? How’s this different from my answer. By the way E and Lambda are not preallocated properly.

zeros would create a scalar not a vector

Answer 2

[madhan ravi]

h = 34.869 ;
c = 13.679 ;
J2eV = 0.845 ;
lambda = 800:6:854;
E = ((h * c) ./ lambda) / J2eV ;
compose("Energy in eV: %f", E((E > 0.673) & (E < 0.678)))

[madhan ravi]

h = 34.869 ;
c = 13.679 ;
J2eV = 0.845 ;
counter = 0 ;
[Lambda, E] = deal(zeros(800:6:854));
for lambda = 800:6:854
    counter = counter + 1 ;
    Lambda(counter) = lambda ;
    E(counter) = ((h * c) / lambda) / J2eV ;
    if ((E(counter) > 0.673) && (E(counter) < 0.678))
       disp('Energy in eV')
    end
end
E 
Lambda