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Roots of a function: Difference between revisions
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ok</pre>
=={{header|ERRE}}==
<lang ERRE>
PROGRAM ROOTS_FUNCTION
!VAR E,X,STP,VALUE,S%,I%,LIMIT%,X1,X2,D
FUNCTION F(X)
F=X*X*X-3*X*X+2*X
END FUNCTION
BEGIN
X=-1
STP=1.0E-6
E=1.0E-9
S%=(F(X)>0)
PRINT("VERSION 1: SIMPLY STEPPING X")
WHILE X<3.0 DO
VALUE=F(X)
IF ABS(VALUE)<E THEN
PRINT("ROOT FOUND AT X =";X)
S%=NOT S%
ELSE
IF ((VALUE>0)<>S%) THEN
PRINT("ROOT FOUND AT X =";X)
S%=NOT S%
END IF
END IF
X=X+STP
END WHILE
PRINT
PRINT("VERSION 2: SECANT METHOD")
X1=-1.0
X2=3.0
E=1.0E-15
I%=1
LIMIT%=300
LOOP
IF I%>LIMIT% THEN
PRINT("ERROR: FUNCTION NOT CONVERGING")
EXIT
END IF
D=(X2-X1)/(F(X2)-F(X1))*F(X2)
IF ABS(D)<E THEN
IF D=0 THEN
PRINT("EXACT ";)
ELSE
PRINT("APPROXIMATE ";)
END IF
PRINT("ROOT FOUND AT X =";X2)
EXIT
END IF
X1=X2
X2=X2-D
I%=I%+1
END LOOP
END PROGRAM
</lang ERRE>
Output (in single precision):
{{out}}
<pre>
VERSION 1: SIMPLY STEPPING X
ROOT FOUND AT X = 8.866517E-07
ROOT FOUND AT X = 1.000001
ROOT FOUND AT X = 2
VERSION 2: SECANT METHOD
EXACT ROOT FOUND AT X = 1
</pre>
=={{header|Fortran}}==
{{works with|Fortran|90 and later}}
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