# Calculating values from an iterative map

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Ollie on 13 Aug 2015
Edited: Ollie on 13 Aug 2015
I need to write a Matlab code that will calculate the x10 value for the following iterative map that doesn't use fsolve,\ or inv commands, given x0= -3.
I also need a code that will calculate:
for the same iterative map.
Any help would be very appreciated :)
Ollie on 13 Aug 2015
Thanks, I think I understand how to do the first part now although I am still struggling with the second part. Is there anyone who could give me the specific code to program it?

Walter Roberson on 13 Aug 2015
Use a "for" loop. Inside the "for" use "if" and "elseif".
Walter Roberson on 13 Aug 2015
x(1) = 0;
for n = 1 : 10
xn = x(n);
first_expression = some calculation with xn
second_expression = some other calculation with xn
if first_expression < second_expression
xn1 = some result calculated with xn
else
....
if third_expression < fourth_expression
...
xn1 = ...
else
...
xn1 = ....
end
end
x(n+1) = xn1
end
Ollie on 13 Aug 2015
Edited: Ollie on 13 Aug 2015
Thanks for the reply. This is the code I have attempted:
x(1)=-3;
for n = 1:10
xn = x(n);
expression1 = xn^4 + 8;
expression2 = 1/(xn*sqrt(abs(xn)));
expression3 = 3 - xn^2;
if expression1 <= expression2
xn1 = sqrt(abs(xn)) - 3*xn
else
if expression3 <= expression2
xn1 = -1/xn*tan(xn)
else
xn1 = -3/xn
end
end
x(n+1)=xn1
end
The code is not returning the correct result. Can you tell me how to fix it?

Purushottama Rao on 13 Aug 2015
for the second part,
s=0;
for n=4:8
k=(x(n-1)-2)+(x(n-1)+1);
s=s+k;
end
disp(s)
Ollie on 13 Aug 2015
Thank you

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