# Shnidman’s equations

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Meshaal Mouawad on 6 Oct 2019
Commented: Honglei Chen on 7 Oct 2019
the Shnidman’s equations in matlab plot SNR vs pfa but I want to plot SNR vs N pulses
for example the probability of detection, a Swerling 1 target, three different probabilities of false alarm, Pd = 0.98; Swerling 1target; PFA = 10^‐8 ,10^‐6, 10^‐4
; N = 1 to 50
I am new to matlab and would love to know how to plot this

Honglei Chen on 7 Oct 2019
In this case you can use shnidman to compute the SNR as a functionof N and then plot it manually, e.g.
N = 1:50;
Pd = 0.98;
Pfa = 1e-6;
SNR = zeros(size(N));
for m = 1:numel(N)
SNR(m) = shnidman(Pd,Pfa,m,1);
end
plot(N,SNR);
xlabel('Number of Pulses');
ylabel('SNR (dB)')
HTH

Honglei Chen on 7 Oct 2019
First of all, your code didn't error out in my machine. It probably didn't do what you want, but it didn't error.
I undersatnd that it might be frustrating as you are new to MATLAB, but sometimes you just need to spend some time checking the output of each line and see if it is what you want. For example, you need to understand what : means. By default A:B means generating a vector from A to B with a step size of 1. Therefore if you call it as 1e-8:1e-4, it actually is just one number, 1e-8 since 1e-8+1 already exceeds the upper bound, 1e-4. You can find this out by checking what Pfa is.
For your purpose, you may want to define Pfa as a vector containing all the numbers you want, then pass those value individually to compute SNR_1, SNR_2, and SNR_3. Then your code will work.
HTH
Meshaal Mouawad on 7 Oct 2019
I got it ! by defining Pfa = [Pfa1 Pfa2 Pfa3 ...etc] where Pfa's is the number of Pfa nedded exp: [1e-3 1e-4 1e-5]
N = 1:50;
Pd = 0.98;
Pfa = [1e-8 1e-3 1e-5];
SNR_1 = zeros(size(N));
SNR_2 = zeros(size(N));
for m = 1:numel(N)
SNR_1(m) = shnidman(Pd,Pfa(1),m,1);
SNR_2(m) = shnidman(Pd,Pfa(2),m,1);
SNR_3(m) = shnidman(Pd,Pfa(3),m,1);
end
plot(N,SNR_1);
hold on
plot(N,SNR_2);
plot(N,SNR_3);
xlabel('Number of Pulses');
ylabel('SNR (dB)')
Honglei Chen on 7 Oct 2019
very nice, glad you got it