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Writing and Analytical

Resources

Lecture 10

Abdisalam Issa-Salwe

Taibah University

College of Computer Science & Engineering

Computer Science Department

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Outline

1. Dimensions and units

2. Graphing

3. Plot

4. Reporting data in text or tables

5. Random Error

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Dimensions and units

� We usually consider quantities like mass, length, time, and perhaps charge and temperature, as fundamental dimensions.

� We then express the dimensions of other quantities like speed, which is length/time, in terms of the basic set.

� Every quantity which is not explicitly dimensionless, like a pure number, has characteristic dimensions which are not affected by the way we measure it.

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Dimensions and units (cont…)

� Units give the magnitude of some

dimension relative to an arbitrary standard.

� For example, when we say that a person is six feet tall, we mean that person is six times as long as an object whose length is defined to be one foot.

� In contrast to dimensions, of which only a

few are needed, there is a multitude of

units for measuring most quantities.

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Dimensions and units (cont…)

� Dimensionless quantities should be easier,

in that they do not have units at all, but in

some ways they are more complicated.

Some examples: Ratios, Angles,

Pressure,

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Graphing

� To be useful, the results of a scientific investigation or technical project must be communicated to others in the form of an oral presentation, technical report, journal article or monograph.

� Effective communication often requires figures, such as photographs, drawings, or graphs, in addition to words and equations.

� When choosing the type of figure to use, start with the type of data you have collected or intend to collect, and the type of information that you intend to convey.

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Graphing (cont..)

� If a graph is appropriate, you need to make conscious decisions regarding several features in order to maximize its effectiveness.

� Decide exactly what type of relationship you want to depict - what would be the purpose of the figure?

� Examine the data, identify the independent and dependent variables and the units Select a plot type

� Select an appropriate scale for each axis and plot the data

� Adjust axis proportions to optimize effectiveness of the figure

� Check plot symbols, add a descriptive line and/or error bars if appropriate Prepare a legend if necessary

� Write out and place the caption

� If computer graphics are used, check the figure carefully and remove any features that do not belong

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Plot

� The purpose of plotting scientific data is to

visualize variation or show relationships

between variables, but not all data sets

require a plot.

� If there are only one or two points, it is

easy to examine the numbers directly, and

little or nothing is gained by putting them

on a graph

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Reporting data in text or tables

� Assuming that you have a normal

distribution, a set of data for a single

sample can be written in text or in a table

as mean ± error, which is usually either

the standard deviation or the standard

deviation of the mean (e.g., 9.8 ± 0.02 m/s

2).

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Random Error

� Random error, known also as experimental error, contributes uncertainty to any experiment or observation that involves measurements.

� One must take such error into account when making critical decisions.

� When you present data that are based on uncertain quantities, people who see your results should have the opportunity to take random error into account when deciding whether or not to agree with your conclusions.

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Random Error (cont…)

� Without an estimate of error, the

implication is that the data are perfect.

� Random error plays such an important role

in decision making, it is necessary to

represent such error appropriately in text,

tables, and in figures.

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Random Error (cont…)

� To represent random error, we

commonly use what we call an error

bar, consisting of a vertical line that

extends from the mean value in

proportion to the magnitude of the error.

� The most common type of error bar that

you will encounter includes a "cap" that

clearly indicates the end of the bar in each

direction.

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References

� Introductory Laboratory Courses in

Biochemistry & Cell Biology,

syllabushttp://www.ruf.rice.edu/~bioslabs/b

ios211/index.htm

� Abdisalam Issa-Salwe lecture notes,

Taibah University.