# Some basic MATLAB questions

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Jonathon on 11 Sep 2012
Commented: nejib on 21 Aug 2023
Okay, so I'm just starting to use MATLAB for engineering assignments. The assignment from my instructor requires us to write a loop using if, else if and else commands. Thats not what I have trouble with, but I need some assistance to come up with a way to take a number and assign it a letter grade based on the number. So the grading scale is like this:
0-59 - F 60-69 - D 70-79 - C 80-89 - B 90-100 - A
So I know I will start the first condition with if, but could someone do an example to show me how it is supposed to be set up? Please DO NOT do the whole thing, as I want to learn it on my own, but sometimes we need a bit of assistance.
Thank you
EDIT: Thanks to Matt for the first Question.
Naftali on 18 Feb 2013
Edited: Walter Roberson on 18 Feb 2013
% n - input numbers in array
k = min(max(floor(0.1*(n-50)+1,1),5) ;

Matt Fig on 11 Sep 2012
Edited: Matt Fig on 11 Sep 2012
X = round(rand*6)
if X<3
disp('Small X')
elseif X==3
disp('X is 3')
elseif X>=3 & X<5
disp('Medium X')
else
disp('X is 5 or 6')
end
nejib on 21 Aug 2023
hello :
i need to have the the same amplitude!!!!
any help : !!
>> t = 0:1/1e3:10;
d = [0:2:60;sin(1*pi*0.1*(0:2:60))]';
x = @rectpuls;
y = pulstran(t,d,x);
plot(t,y)
hold off
xlabel('Time (s)')
ylabel('Waveform')
>>

Matt Tearle on 11 Sep 2012
Thank you for your asking such a great question! Matt has basically given you all the info you need for this assignment, but, in the spirit of Sean's "not what you were asked, but some cool stuff you should know about MATLAB"...
x = randi(100,20,1) % Make some grades
y = char(70*ones(size(x))); % Everyone gets an F!
y(x>59) = 'D' % Upgrade the Ds (and better)
y(x>69) = 'C' % Upgrade the Cs
y(x>79) = 'B' % The Bs
y(x>89) = 'A' % And finally the As
Or (requires Stats TB, which you should have as a student)
y = ordinal(x,{'F','D','C','B','A'},[],[0,60:10:100])
mean(x(y>='C')) % The average score of those who got a C or better
Sean de Wolski on 11 Sep 2012
+1: ordinal can behave like histc(). Learn something every day

Matt Fig on 11 Sep 2012
Edited: Matt Fig on 11 Sep 2012
As per requested:
% x is the numerical unknown grade
G = char(interp1([-inf,59,60,69,70,79,80,89,90,inf],['FFDDCCBBAA'],x,'n'))
or, for 2012+ versions:
G = char(interp1([-realmax,59,60,69,70,79,80,89,90,realmax],double(['FFDDCCBBAA']),x,'n'))

Matt Fig on 11 Sep 2012
Edited: Matt Fig on 11 Sep 2012
Another one-liner (short!):
% x is the unknown numerical grade.
G = char(65+sum(x<.5+[59 59:10:89]));
As it stands it only works for scalar x. BSXFUN would cure that if it was needed, like so.
G = char(65+sum(bsxfun(@lt,x,.5+[59 59:10:89].')));

Sean de Wolski on 11 Sep 2012
Edited: Sean de Wolski on 11 Sep 2012
I know this is not the purpose of your assignment, but here is a cool way to do it. The logic should be easily transmittable to if/else/etc instead of histc()
letters = 'FDCBA';
letters(idx)
Matt Fig on 11 Sep 2012
Now why would support for inf be dropped? TMW does some strange stuff from time to time. (strmatch, findstr, etc...)

Jan on 11 Sep 2012
index = max(1, ceil(-4.9:0.1:5.1));
pool = 'FDCBAA';

Yash Meshram on 24 Oct 2019
i = input('Marks of the student: ');
if 0<=i && i<=59
end
if 60<=i && i<=69
end
if 70<=i && i<=79
end
if 80<=i && i<=89
end
if 90<=i && i<=100
end

hassan saher on 24 Dec 2020
Use help command to get help about rand function.

Vivek Sharma on 8 Jun 2021
Thank you.
mahmood on 17 May 2023
Edited: DGM on 18 May 2023
clc;
clear;
% Constants
c = 13.03;
p = 19.93;
% Initial temperatures
T1 = 576;
T2 = 439;
% Number of impacts
m = 5;
% Initialize variables
T = (T1 + T2) / 2;
E = zeros(m, 1);
% Perform m impacts
for i = 1:m
E(i) = (c * p * T) / 23.5;
T = (T1 + T) / 2;
end
% Display the values of E for each impact
disp('Values of E for each impact:');
disp(E);

nejib on 21 Aug 2023
>> t = 0:1/1e3:10;
d = [0:2:60;sin(1*pi*0.1*(0:2:60))]';
x = @rectpuls;
y = pulstran(t,d,x);
plot(t,y)
hold off
xlabel('Time (s)')
ylabel('Waveform')
>>
??? >>