I was asked to write a matlab code to calculate the mean of 5 numbers utilizing a loop structure, I wrote this code but I was wondering if I could do something to make matlab ask me to enter the values in order 1 to 5, for example " Enter Value 1 " " Enter Value 2" , etc.
sumx = 0;
N = 5;
i=1;
for n =1:N
i=i+1;
Valuei=input('Enter Values= ');
sumx = sumx+Valuei;
end
Ybar=sumx/5;
display(Ybar);
You need sprintf:
N = 5;
for n = 1:N
prompt = sprintf('Enter Value %d=', n);
Value = input(prompt);
...
end
The %d is replaced by the value of n for each iteration of the loop.
Also, the variable i isn't used. You can get rid of it. It's a bad idea to use i (or j) as a variable name anyway since it's already defined by Matlab to be the imaginary unit.
Related
I'm writing a program that finds the indices of a matrix G where there is only a single 1 for either a column index or a row index and removes any found index if it has a 1 for both the column and row index. Then I want to take these indices and use them as indices in an array U, which is where the trouble comes. The indices do not seem to be stored as integers and I'm not sure what they are being stored as or why. I'm quite new to Matlab (but thats probably obvious) and so I don't really understand how types work for Matlab or how they're assigned. So I'm not sure why I',m getting the error message mentioned in the title and I'm not sure what to do about it. Any assistance you can provide would be greatly appreciated.
I forgot to mention this before but G is a matrix that only contains 1s or 0s and U is an array of strings (i think what would be called a cell?)
function A = ISClinks(U, G)
B = [];
[rownum,colnum] = size(G);
j = 1;
for i=1:colnum
s = sum(G(:,i));
if s == 1
B(j,:) = i;
j = j + 1;
end
end
for i=1:rownum
s = sum(G(i,:));
if s == 1
if ismember(i, B)
B(B == i) = [];
else
B(j,:) = i;
j = j+1;
end
end
end
A = [];
for i=1:size(B,1)
s = B(i,:);
A(i,:) = U(s,:);
end
end
This is the problem code, but I'm not sure what's wrong with it.
A = [];
for i=1:size(B,1)
s = B(i,:);
A(i,:) = U(s,:);
end
Your program seems to be structured as though it had been written in a language like C. In MATLAB, you can usually substitute specialized functions (e.g. any() ) for low-level loops in many cases. Your function could be written more efficiently as:
function A = ISClinks(U, G)
% Find columns and rows that are set in the input
active_columns=any(G,1);
active_rows=any(G,2).';
% (Optional) Prevent columns and rows with same index from being simultaneously set
%exclusive_active_columns = active_columns & ~active_rows; %not needed; this line is only for illustrative purposes
%exclusive_active_rows = active_rows & ~active_columns; %same as above
% Merge column state vector and row state vector by XORing them
active_indices=xor(active_columns,active_rows);
% Select appropriate rows of matrix U
A=U(active_indices,:);
end
This function does not cause errors with the example input matrices I tested. If U is a cell array (e.g. U={'Lorem','ipsum'; 'dolor','sit'; 'amet','consectetur'}), then return value A will also be a cell array.
I am new to matlab and I have couple of questions about it. First one, "Your function should terminate the sequence when either the value of ... or..." I use || in the code but it does not work as expected while && gives me the correct answer. Second question, how could the code be to display only the final answer?
Problem: calculate X which is represented by the sequence below
X = 1 - 1/2^2 + 1/3^2 - 1/4^2 +....
Requirement: Your function should terminate the sequence when either the value of 1/k^2 is less than 0.0001 or k is equal to k_max.
input k
Initialize x = 0
for loop i from 1 to k
if 1/i^2<0.0001 && i >= 100
break
end
Calculate X = (-1)^(i+1)./i^2 + X
end
You can use the break function as follows, where END_CONDITION is the condition you want to end your loop in.
if END_CONDITION
disp(X);
break;
end
To display the final answer, you can use the disp function. Eg. if your variable you want to print is called A then you use the following code.
disp(A)
Collectively this is your code. Since k_max terminates at the end of the for loop, we don't have to add any conditions to break out of the loop.
X = 0;
for i = 1:k
if 1/i^2<0.0001 || i==100
break;
end
X = (-1)^(i+1)./i^2 + X;
end
disp(X);
The general syntax for a for loop in Matlab is :
for j = 1 to 5
%body
end
I want to have a variable whose value is calculated at run time depending on the user input to be used for controlling the number of times the for loop is to be run.
So I want to have:
m = input('Some Message');
n = ....% Some Calculations using user input 'm'
for j = 1 to n
%body
end
I tried this, but am getting an error -
Undefined function 'to' for input arguments of type 'char'.
Matlab is considering the variable n as a character instead of a variable.
P.S: I am new to Matlab, I searched a lot online, but couldn't get a solution for this. Please help.
The error message seems quite readable. This it not valid Matlab syntax. You would write a for loop of n repititons like this
m = input('Some Message: ');
if strcmp(m, 'foo')
n = 7;
else
n = 5;
end
for j = 1:n
fprintf('%d\n', j);
end
Actually, have you tried this syntax:
for j=1:n
%body
end
I don't see the word "to" in the docs. So the for loop syntax you have above would not be valid Matlab syntax. The other thing to consider is that n is being interpreted as a character and not a number.
I have a little parfor test script which gives the warning in the title.
The code is this
out = zeros(10, 1);
in = rand(5e8, 10);
tic
parfor i = 1:10
for j = 1:5e8
p = floor(rand(1,1)*5e8);
out(i) = out(i) + in(p, i);
end
end
toc
tot = sum(out)
the warning comes out on line 7 regarding how variable in is accessed.
I don't understand why, slicing should be trivial. Just send each column of in to each worker.
If I change the code to
out = zeros(10, 1);
in = rand(5e8, 10);
tic
parfor i = 1:10
a = in(:,i);
for j = 1:5e8
p = floor(rand(1,1)*5e8);
out(i) = out(i) + a(p);
end
end
toc
tot = sum(out)
the warning disappears but I don't like that assignment to a.
The code was explicitly designed to mess up the cache memory.
Unfortunately, as explained here http://www.mathworks.com/help/distcomp/advanced-topics.html#bq_of7_-1 , MATLAB does not understand how to slice in, hence the code analyser warning. You have to read that page fairly closely to understand why it cannot be sliced. The relevant paragraph is:
Form of Indexing. Within the list of indices for a sliced variable, one of these indices is of the form i, i+k, i-k, k+i, or k-i, where i
is the loop variable and k is a constant or a simple (nonindexed)
broadcast variable; and every other index is a scalar constant, a
simple broadcast variable, colon, or end.
The clause in bold type at the end is the relevant one - in your case, p does not match this constraint.
I have one program that has function and the problem, return value, it has too many output.
Like exempley: y = text the answer comes up
Error in text (line 2)
if nargin == 0
Output argument "array" (and maybe others) not assigned during call to "
C:\Users\name\Documents\MATLAB\text.m>text".
The program text.m reads a txt file that contains a couple of names and numbers like
exemple:
John doughlas 15986
Filip duch 357852
and so on. The program convert them to 15986 Doughlas John and so on.
function array = text(~)
if nargin == 0
dirr = '.';
end
answer = dir(dirr);
k=1;
while k <= length(answer)
if answer(k).isdir
answer(k)=[];
else
filename{k}=answer(k).name;
k=k+1;
end
end
chose=menu( 'choose file',filename);
namn = char(filename(chose));
fid = fopen(namn, 'r');
R = textscan(fid,'%s %s %s');
x=-1;
k=0;
while x <= 24
x = k + 1;
All = [R{3}{x},' ',R{1}{x},' ',R{2}{x}];
disp(All)
k = k + 1;
end
fclose(fid);
Is there anyway to fix the problem without starting over from scratch?
Grateful for all the answers!
You specify the function output argument in the definition, but you don't assign anything to it in the function body.
For example, in
function y = student(j)
your output is y. So you have to assign something to y.
Read more about functions in MATLAB.
Here is a working example.
The first part is to create a function called 'functionA' in a filename 'functionA.m'. Then put the following code inside:
function result = functionA(N,alpha)
result = 5;
return
end
The second part is to create another Matlab file(i.e. upto you to name it) or you can use the Matlab command window even. Then run the following code:
getresult = functionA(100,10);
getresult
After running you get the following answer:
ans =
5