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while

while. The general form for while is : while expression statement end Example : >> A=[1 2 ; 3 4]; >> while det(A)==-2; A=A./2; end; >> A A = 0.5 1 1.5 2.

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while

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  1. while • The general form for while is : while expression statement end Example : >> A=[1 2 ; 3 4]; >> while det(A)==-2; A=A./2; end; >> A A = 0.5 1 1.5 2

  2. Question. Find the largest natural number n such that 5n ≤ 55. Answer. >> n=0; m=55; >> while 5*n<m n=n+1; end >> n n= 11

  3. Example : >> S=[1 2]; k=9; >> while max(S)==2; k=k+1, end; As you see, because the expression is always satisfied, this cause a repeating process. To stop the process, use CTRL + C Next, we will learn to break the process, if a condition is satisfied.

  4. if and break The general form for if is : • if relation statements end or • if relation statements elseif relation statements else statements end

  5. Note : After all statements put comma (,) or semicolon (;) Examples : >> r=6; >> if r==6; k=12+r, end; k= 18 >> if k>18 s=2*k, elseif k<18 s=k+1, else s=1, end s= 1

  6. BREAK >> S= [ 1 1 2]; n=5; >>while max(S)==2; n=n+1, if n==10, break , end, end; n = 6 n = 7 n = 8 n = 9 n = 10

  7. TRY THIS For a given two matrices A and B, the expression A is not equal to B must be written as follows. >> A= [1 2 ; 3 4 ]; B= [ 1 4 ; 2 5]; >> if A~=B k=4, elseif any(any(A~=B)) k=7, else k=3, end k= 7 As it seen, even if an entry of matrices are equal, Matlab assumes these two are not exactly different. Or for inequality of two matrices, write the command as follows >> if A==B k=3, else k=7, end k= 7

  8. Vector functions max(A) and min (A) : If A is a vector (row or column), these commands gives the maximum or minimum entries. If A is a mxn matrix (m≥2), then the command gives the row where maximum or minimum value is entered. >> A=[1 2; 3 4]; >>max(A) ans= 3 4 >>max(max(A)) ans= 4

  9. sum : gives the sum of entries of a column prod : gives the product of entries >>A=[ 1 2 ; 3 4] >> prod(A) A= 1 2 ans= 3 4 3 8 >> sum (A) >> D=prod(prod(A)) ans= D= 4 6 24 >> sum(sum(A)) ans= 10

  10. median, mean, std, sort • median : For vectors, median(A) is the median value of the elements in A.For matrices, median(A) is a row vector containing the medianvalue of each column. • mean : mean value • std : standard deviation • sort : sorts the elements in column of A in ascending order Example : >> H=[ 1 3 ; 3 2; 2 5]; >> sort(H) • ans= 1 2 2 3 3 5

  11. any, all • any : True if any element of a vector is a nonzero number or islogical 1 (TRUE). ANY ignores entries that are NaN (Not a Number). • all : True if all elements of a vector are nonzero. • Example :>> F=[ 0 1 2 ; 0 0 3 ; 0 1 4] F = 0 1 2 0 0 3 0 1 4 >>any(F) ans= 0 1 1 >>all(F) ans= 0 0 1

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