Basic queries Matlab (vectors, indexing, construct matrices in a specific form)

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Abderrahmane Elakhiri 2020-5-24

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/531683-basic-queries-matlab-vectors-indexing-construct-matrices-in-a-specific-form

评论： Abderrahmane Elakhiri 2020-5-27

Hello community,

I am beginner in Matlab. I am struggling with the following exrcises. I only managed to answer 1 & 5 however the others confuse me and I don't even know how to start specially with 2 & 3. Please I need your help

My solutions:

%Exercise 1
x = [2:3:89]
%Exercise 5
function density=ExamC()
x=input('Please enter x: ');
m=input('Please enter mean: ');
s=input('Please enter standard deviation: ');
f=1/(s*sqrt(2*pi))*exp(1)^((1/2)*((x-m)/s)^2);
disp('Value of density is: '), disp(f);
end

Thank you for your help,

Abdel

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Abderrahmane Elakhiri 2020-5-24

Thank you very much @Stephen Cobeldick!

It was very easy to do:

%Exercise 2:
vec = [1 2 3 4 5 6 7 8 9 10];
vec(rem(vec,2)==0)=5;

per isakson 2020-5-24

Or

%Exercise 2:
vec = [1 2 3 4 5 6 7 8 9 10];
vec( 2 : 2 : end ) = 5;

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Answer 1

per isakson 2020-5-24

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/531683-basic-queries-matlab-vectors-indexing-construct-matrices-in-a-specific-form#answer_437848

Exercise 1 and 2

"[...] however it confuses me the way the question is written!" Agree; the very same vector has three different names, x, vec and v. (It might be about level of abstraction; an effort to distiguish between the vector and its representation in Matlab.)

Exercise 3.

The text is ok.

Exercise 4.

There are relevant examples in the documentation on plot()

Exercise 5.

The statement

function density=ExamC()

doesn't follow the instruction. The last sentence says

function f = density( x, m , s )

(to my best understanding)

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Abderrahmane Elakhiri 2020-5-27

Thank you and apologize for the late reply.

I managed to solve all of them, and you are right for question 5, it's:

function f = density (x, m, s)

I used ExamC instead of density on purpose.

Solutions for all exercises I posted in case someone needs them:

%Exercise 1
x = [2:3:89]
%% 
%Exercise 2
vec = [1 2 3 4 5 6 7 8 9 10];
vec(rem(vec,2)==0)=5; % solution 1
vec(2:2:end)=5 % solution 2
%%
%Exercise 3
A=rand(1,5); B=rand(4,2); C=rand(2,3); D=rand(2,3);
E=[A;[B,[C;D]]];
%%
%Exercise 4
x=linspace(-4,8,200);
y=sin(x);
y2=sin(2*x);
y3=sin(3*x);
plot(x,y,'red',x,y2,'black',x,y3,'green')
ylim([-1.5 1.5]);
%%
%Exercise 5
function f=density()
x=input('Please enter x: ');
m=input('Please enter mean: ');
s=input('Please enter standard deviation: ');
f=1/(s*sqrt(2*pi))*exp(1)^((1/2)*((x-m)/s)^2);
disp('Value of density is: '), disp(f);
end
%%