computer programming (tkk-2144) 13/14 semester 1 instructor: rama oktavian email:...
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Computer Programming(TKK-2144)
13/14 Semester 1
Instructor: Rama OktavianEmail: [email protected] Hr.: M.13-15, W. 13-15 Th. 13-15, F. 13-15
Outlines
1. Interpolation: Basic Theory 1. Interpolation: Basic Theory
2. Methods of interpolation 2. Methods of interpolation
3. Interpolation in Excel 3. Interpolation in Excel
4. Interpolation in chem.eng 4. Interpolation in chem.eng
Interpolation (basic theory)
Interpolation function
a function that passes exactly through a set of data points.
Interpolating functions to interpolate values in tables
find functional values at other values of the independentvariable, e.g. sin(0.63253)
Interpolation (basic theory)
Interpolation
1. Linear Interpolation
2. Polynomial Interpolation
3. Cubic Spline Interpolation
4. Lagrange Polynomial Interpolation
Interpolation methods
Linear Interpolation
Linear interpolation is obtained by passing a straight line between2 data points
)(xfthe exact function for which values are known only at a discrete set of data points
)(xg the interpolated approximation to )(xf
10 , xx the data points(also referred to as interpolation points or nodes)
Interpolation methods
Linear Interpolation
If is a linear function then)(xg bAxxg )(
To pass through points and ))(,( 00 xfx ))(,( 11 xfx
)()()()( 0101
00 xfxf
xx
xxxfxg
Interpolation methods
Linear Interpolation
Advantages:• Easy to use (homework, exams)• Exact for linear functions
Disadvantages:• Not very accurate for nonlinear functions
Interpolation methods
Polynomial Interpolation
Two steps:
• obtain polynomial coefficients
• evaluate the value of the polynomial at the desired location (xi)
For N data points, there is a unique polynomial (usually of order n-1) that goes through each point
This is an interpolating polynomial, because it goes exactly through each data point
Interpolation methods
Polynomial Interpolation First step:
• obtain polynomial coefficients
For general n, the goal is to determine the coefficients a1, a2,…,an so that for all i = 1:n
iin yxp )(1
Pn-1(x) = a1 + a2x + a3x2 +…+ anxn-1
Writing these equations in matrix-vector form, we obtain
Vandermonde matrix
Interpolation methods
Polynomial Interpolation Second step:
• evaluate the value of the polynomial at the desired location (xi)
iin yxp )(1
Pn-1(xi) = a1 + a2xi + a3xi2 +…+ anxin-1
Sin(0.63) = ??
Interpolation in excel
Lookup Tables
• Often, we need to retrieve data that is stored in a table
• For example, consider these tables:
Interpolation in excel
LOOKUP(Lookup_value,Lookup_vector,Result_vector)
search downthe lookupvector
find eithera matchingvalue, ora valuegreater thanthe lookupvalue, whicheveroccurs first go to the same position in
the result vector, and extractthe value there
Interpolation in excel
Metal Modulus of Elasticity, psi Density, lb/in3 Yield Strength, psi
Aluminum 2014-T6 10,600,000 0.101 60,000
Aluminum 6061-T6 10,000,000 0.098 37,000
Stainless Steel 304 28,000,000 0.284 30,000
Structural Steel A36 29,000,000 0.284 36,000
Since the properties to be retrieved are in columns, the table is called a vertical lookup table
The vertical lookup table command in Excel is:VLOOKUP(lookup value, table range, column number, true/false)
Interpolation in excelVLOOKUP(Lookup_value,Table_array,col_index_num,Range_lookup)
searchdownleftcolumnoftablearraytofindmatch
Which column number forextraction of result? 1, 2, 3 or 4?
result
optional argument:if FALSE, requiresan exact match
Interpolation in excel
Examples
Using VLOOKUP to find the freezing point of a 33% solution
The formula
=VLOOKUP(F3,$A$3:$D$54,2,0)
Interpolation in excel
Other ways to Lookup Tables
Match(Lookup_value, lookup_array, match type)
Returns the relative position in the array that matches the
lookup value.
Index(range, position)
Returns the value from the range in the position specified
Interpolation in excel
Example
use the MATCH function to find the position of the maximum value in the range
MATCH(lookup_value,lookup_array,match_type_num)
=MATCH(83119,$B$5:$B$16,0)
Interpolation in excel
Example
use the INDEX function to return the value in the same position in the array of months:
=INDEX( $A$5:$A$16,4)
=INDEX( $A$5:$A$16, MATCH( MAX( $B$5: $B$16), $B$5:$B$16,0))
Interpolation in excel
Lookup value for two-way tables
=VLOOKUP(Temp,Table, MATCH( Percent, P-Row, 1 )+ 1,1)
=VLOOKUP( M2, $A$4:$1$32, MATCH( N2, $B$3:$K$3,1 )+1, 1)
Interpolation in excel
A Note About Lookup Tables
Lookup tables will not interpolate values!
When looking up a numerical value, if an exact match is not
found (and the “TRUE” option allows for an approximate
match), then the value searched for is rounded down to the
next tabulated value.
We will illustrate this in the following example
Interpolation in excel
Example
The population data of a town is given in the table
We want to use a lookup table to report the population for any year entered
Interpolation in excel
Example
Note that using the VLOOKUP function (with the TRUE/FALSE option left off or set to TRUE) returns the population for the next year in the table lower than the input value:
Interpolation in excel
Linear interpolation in excel
For each population interval, construct an IF statement to see if the input year falls within the interval range…
If the input year is within the interval, then the interpolation formula should be used…
If the input year is not within the interval, then a space is entered into the cell to make it blank.
Interpolation in excel
Linear interpolation in excel IF statements add a great deal of flexibility to Excel
spreadsheets – allow control over how calculations are performed
Lookup tables are convenient for accessing data that is stored in table form. Important to remember that lookup tables do not interpolate between values
Linear interpolation formulas can be added to tables in order to provide a better estimate of values between tabulated points
Interpolation in excelApplication of VLOOKUP: Linear interpolation from a table of physical properties
For any %HNO3
from 0 to 90, wewant an automaticestimate of theheat capacity
Interpolation in excelApplication of VLOOKUP: Linear interpolation from a table of physical properties
Create index columns to the right and left of the table
Interpolation in excelApplication of VLOOKUP: Linear interpolation from a table of physical propertiesEnter VLOOKUP functions based on “NitricTable2” and using the low and high row indices to extract the bracketing values of %HNO3 and Heat Capacity.
Interpolation in excel
LowPct HighPct
LowHC
HighHC
linear approximationbetween to locationsin the table
input%HNO3
HeatCapestimate
input LowPct
HeatCap HighHC LowHC LowHCHighPct LowPct
Interpolation in excelChange values of the input to get different results
[including bad results when input outside ofacceptable range]
the good the bad and the ugly!
Interpolation in excelLinear Interpolation using TREND function
TREND can be used to perform linear interpolation between two adjacent data points.
TREND( known_y's, known_x's, new_x 's, const)
=TREND( B20: B21 , A20:A21, F18,1)
Interpolation in excelLinear Interpolation in a Two-way Table
Find the viscosity value in the table for x = 76°F, y = 56.3 wt% ethylene glycol
Interpolation in excelLinear Interpolation in a Two-way Table
First step, interpolate the value at y = 56.3
Second step, interpolate the value at x = 76
ExtrapolationDefinition
The process of taking data values at points x1, ..., xn, and approximating a value outside the range of the given points.
The process of estimating and forecasting
Sin (2.6) = ??
ExtrapolationMethods
Linear extrapolation
If the two data points nearest the point to be extrapolated are and , linear extrapolation gives the function:
Polynomial extrapolation
ExtrapolationMethods
Linear extrapolation
Given the following data which is known to be linear, extrapolate the y value when x = 2.3.
(0.3 0.80), (0.7, 1.3), (1.2, 2.0), (1.8, 2.7)
Interpolation in Chem. Eng
Example - Vapor Pressure of Water
Determine vapor pressure of water at:• 25 °C• 92 °C• 105 °C
Interpolation in Chem. Eng
Example - “Real” Gases
zRTVp ˆ
p- pressurez- compressibility factorR- gas constantT- temperature - Molar volumeV̂
Find z at T = 725K and p = 8bar.