Why am I getting invalid expression?

Question

Gina Jarid 2020-10-1

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/603349-why-am-i-getting-invalid-expression

编辑： John D'Errico 2020-10-1

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

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Answer 1

drummer 2020-10-1

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https://ww2.mathworks.cn/matlabcentral/answers/603349-why-am-i-getting-invalid-expression#answer_503740

编辑：John D'Errico 2020-10-1

在 MATLAB Online 中打开

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

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madhan ravi 2020-10-1

编辑：madhan ravi 2020-10-1

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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

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Answer 2

madhan ravi 2020-10-1

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/603349-why-am-i-getting-invalid-expression#answer_503737

编辑：madhan ravi 2020-10-1

在 MATLAB Online 中打开

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)))

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madhan ravi 2020-10-1

在 MATLAB Online 中打开

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