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    R solve() Equation with Examples

    R solve() Equation with Examples

    R solve() is a generic function that solves the linear algebraic equation a %*% x = b for x, where b can be either a vector or a matrix. For example 10 * x = 20, in this equation, 10 is the coefficient; 20 is a constant and solve() calculates x which is 2.

    1. Quick Examples of solve() Function in R

    Following are quick examples of solve() function that solves the different equations.

    
# calculate x using solve()
solve(10, 20)
solve(3, 6)
solve(4, 20)

# with two variables
a <- matrix(c(3,1,4,1),nrow=2,ncol=2)
b <- matrix(c(10,4),nrow=2,ncol=1)
print(a)
print(b)
res <- solve(a,b)
print(res)

# with matrix
a <- c(2, 1) 
b <- c(5, 3) 
xyz <- rbind(a, b) 
print(xyz)
solve(xyz)

# with 4x4 matrix
a <- c(2, 1, 3, 3) 
b <- c(5, 3, 5, 4) 
c <- c(6, 5, 9, 6)
d <- c(1, 3, 2, 2)
xyz <- rbind(a, b, c, d) 
print(xyz)
res <- solve(a=xyz) 
print(res)

    <a id="h-2-solve-syntax"></a>

    2. solve() Syntax

    Below is the syntax of the solve() equation function.

    
# Syntax of solve()
solve(a, b, …)

    The following are the parameters.

    3. R solve() Equation Example

    By using solve() function in R you can solve algebraic equations like a %x% = b. The solve() function takes arguments a and b as arguments and calculates x. Also, use this function to calculate complex equations like finding the value for x and y. Let's see the first example which finds the value of x.

    
# One variable example
# 10x = 20
# What is the x?
solve(10, 20)

# Output
# [1] 2

    Below are some more examples.

    4. R solve() with Matrix

    solve() also takes a matrix as an argument for param a. Let's create two vectors using combine function c(). and using rbind() function let's bind these into a matrix. The below example demonstrates finding values for two variables x and y.

    
# Two variable example
# 3x + 4y = 10
# x + y = 4
# What is x and y?

# Example
a <- matrix(c(3,1,4,1),nrow=2,ncol=2)
b <- matrix(c(10,4),nrow=2,ncol=1)
print(a)
print(b)
res <- solve(a,b)
print(res)

# x value is -6
# y value is 4

    Yields below output. The row and column names of the equation result are taken from the column names of a and of b respectively. If b is missing the column names of the result are the row names of a.

    5. Using Just Param a and default b

    Let's pass the one param a to the R solve() function and leave the b as default.

    
# solve() with matrix
a <- c(2, 1) 
b <- c(5, 3) 
xyz <- rbind(a, b) 
print(xyz)
solve(xyz)

    Yields below output.

    Let's check another example with 4 x 4 matrix.

    
# with 4x4 matrix
a <- c(2, 1, 3, 3) 
b <- c(5, 3, 5, 4) 
c <- c(6, 5, 9, 6)
d <- c(1, 3, 2, 2)
xyz <- rbind(a, b, c, d) 
print(xyz)
res <- solve(b=xyz) 
print(res)

    Yields below output.

    6. Conclusion

    In this article, you have learned R solve() is a generic function that solves the linear algebraic equation a %*% x = b for x, For example 10 * x = 20, in this equation, 10 is the coefficient; 20 is a constant and solve() calculates x which is 2.

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    References