A bar chart represents a certain quantity by unit length, draws straight bars with different lengths according to the quantity, and then arranges these straight bars in a certain order. It is easy to see various numbers from the bar chart. Bar charts are generally called bar charts, also called bar charts or bar charts. Bar charts use the length of the bar to represent the quantity, which is convenient for comparison. Bar charts are divided into bar charts and composite bar charts, which are composed of various data and marked with different colors.

Second, classification

Bar charts can be divided into simple bar charts and composite bar charts. The former only represents the data of 1 item, while the latter can represent multiple items of data at the same time.

Frequency: Generally, we call the number of times the data falls in different groups as the frequency of the group.

Frequency: the ratio of frequency to total data is frequency, and frequency × 100% is percentage.

Third, application

Bar charts are mainly used to represent discrete data, that is, counting data.

The similarity between a single bar chart and a composite bar chart is that people can clearly see the numbers, but the difference is that a single bar chart is used to compare one object, while a composite bar chart is used to compare the number of multiple objects.

Under the same conditions, n experiments were carried out. In these n experiments, the frequency nA of event A is called the frequency of event A. The ratio of nA/n is called the frequency of event A, and it is denoted as fn(A). Its definition is: the ratio of the number of times each object appears to the total number of times is the frequency.

1. When the number of repeated experiments n increases gradually, the frequency fn(A) shows stability and gradually stabilizes at a certain constant, which is the probability of event A. This "frequency stability" is also called statistical regularity.

Frequency is not equal to probability. According to Bernoulli's theorem of large numbers, when n approaches infinity, frequency fn(A) approaches probability P(A) in a certain sense.

English definition: frequency

The relative frequency m/n of random events appearing m times in n tests. In general physical science, frequency refers to the number of vibrations per second, which can be random or deterministic.

Under certain conditions, observing or testing the studied object is called a test every time the condition group is realized. The result is called an event. In experiments, events that may or may not occur are called random events.

The probability p(A) of random event A is a measure of the probability of this event. Its value is between 0 and 1. Under certain conditions, if event A is impossible, then p (a) = 0; If event A must occur, then p(A)= 1. With the increase of test times n, the probability of frequency approaching probability is greater, that is, δ in the formula is an arbitrary decimal value.

Hydrological phenomenon is a complex natural phenomenon, and its occurrence probability cannot be known, which can only be inferred by counting the occurrence frequency in the measured hydrological data. Due to the limitation of data, there will always be some errors.

The random variable X, which describes hydrological stochastic phenomena, generally belongs to continuous type. Therefore, the probability that x equals any number x is p{X=x}. Cumulative percentage curve FX (x) ~ x is used to describe the statistical characteristics of hydrological variables in hydrological calculation. If the probability of annual flood peak discharge at Yichang Station of the Yangtze River is greater than or equal to 80000m3/s, p{X≥80000}=FX(80000).

In hydrological calculation, the frequency density function FX(x) of hydrological variables is generally estimated by statistical analysis based on measured data, and then the cumulative percentage function fX(x) of hydrological variables can be obtained by integrating fX(x) (see figure):

In hydrological calculation, it is customary to call cumulative percentage curve FX(x) as frequency curve and FX (x) ~ x curve as frequency density distribution curve.

Frequency = frequency/total * 100%

Fourth, production.

(1) According to the size of the drawing, draw two straight lines perpendicular to each other as the vertical axis and the horizontal axis.

(2) Distribute the positions of the bars appropriately on the horizontal ray (horizontal axis) and determine the width and spacing of the straight bars.

(3) Determine the unit length on the vertical axis, and mark the quantity mark and measurement unit.

(4) According to the size of the data, draw straight lines with different lengths and mark them with titles.

(5) If the bar is too small, you can draw colors on the bar appropriately.

Verb (abbreviation for verb) function

Can clearly reflect the quantity, easy to compare.